nmg25n3: pecos diamonds--quartz and dolomite crystals …pecos diamonds–quartz and dolomite...

August 2003, Volume 25, Number 3 NEW MEXICO GEOLOGY 63August 2003, Volume 25, Number 3 NEW MEXICO GEOLOGY 63

AbstractPecos diamonds, also known as Pecos valleydiamonds are colorful, doubly terminatedquartz crystals that occur in scattered out-crops of the Permian Seven Rivers Formation(Permian) along the Pecos River valley insoutheastern New Mexico. Although authi-genic quartz is relatively common in evapor-ite sequences worldwide and throughoutgeologic history, Pecos valley diamonds areunique for their large size, variable color,and crystal morphologies. Single crystals ofdolomite of variable morphologies alsooccur with the Pecos valley diamonds butare of much more limited distribution. Redpseudohexagonal aragonite crystals are alsopresent near one locality, but they have notbeen found to coexist in the same unit.

Although the outcrop area encompassesan area 100 mi long by as much as 25 miwide along the margins of the river valley,the distribution of Pecos valley diamonds islimited to specific depositional environ-ments that resemble salinas and/or salt panswithin a larger sabkha setting. Replacementfeatures within the quartz indicate an authi-genic origin with formation soon afterdolomitization of the host rock. However,the large size and suite of inclusions mayindicate a deep burial, late diagenetic originfor these crystals. The presence of organicmatter, formation of dolomite, and the oxi-dation of sulfide appear to be importantcomponents to the ultimate formation ofPecos valley diamonds.

IntroductionColorful and doubly terminated authi-genic quartz crystals with variable crystal-lographic forms occur in and weatheredfrom scattered outcrops of the SevenRivers Formation in southeastern NewMexico (Fig. 1). In places, when the sun’srays are at low angles, the desert appearspaved with diamonds. However, mostsparkles are only broken or small andimperfect crystals. Only a small percentageof crystals are large enough to be of inter-est to the collector. Crystals in a matrix ofgypsum are only rarely found, but atLocality 1, a 10-cm layer consists of a massof quartz crystals.

A Spanish miner, Don Antonio de Espe-jo, first described these crystals in 1583(Albright and Bauer, 1955). In 1929 Tarrdescribed the occurrence near Acme in

DistributionLarge, authigenic quartz and dolomitecrystals appear to be confined exclusivelyto the Permian Seven Rivers Formation.Essentially all occurrences are confined tothe back reef segment of the Guadalupereef complex starting in the south at the“beginning of the gypsum facies” of Kelley(1971) near Dark Canyon and terminatingnear the De Baca and Guadalupe Countyline in the vicinity of Salado Creek to thenorth. In Pecos country, the back reef seg-ment of the Seven Rivers Formation con-sists predominantly of gypsum with sub-ordinate amounts of dolomitic limestone,red and gray gypsiferous shale, and fine-grained sandstone. East of the study area,anhydrite and salt become prevalent. Wardet al. (1986) documented two originaldepositional modes for the gypsum; theseinclude subaqueous salina and subarealsabkha environments.

Meinzer et al. (1927) coined the termSeven Rivers gypsiferous member for thelater discredited Chupadera Formation.Tarr (1929) referred to the authigenicquartz occurrence at Acme (Locality 6) asbeing in the Manzano series of red beds. Inthe same year, Tarr and Lonsdale (1929)continued to use the term ChupaderaGroup in describing the pseudocubic crys-tals near Artesia (Localities 1 and 2). Thesenames were changed to Whitehorse, ChalkBluff, and Bernal by various authors andpetroleum geologists over the years. Sub-sequently, Tait et al. (1962) proposed thepresently used stratigraphic names basedon the nomenclature applied to the subsur-face rocks of the Artesia Group.

Kelley (1971) mapped the surface out-crops of the study area. During his map-ping, Kelley (1971, p. 18) reported, “in timeit was noted that their [the Pecos dia-monds] distribution is stratigraphicallyrelated. This is so commonly true that theymight be used as a stratigraphic indicator.Most all occurrences are in part of a zoneperhaps 100 to 200 feet thick from theupper part of the Seven Rivers into thelower part of the Yates.” Of the 12 in situoccurrences of authigenic quartz crystalsdescribed in this paper, 10 are within amapped area of Kelley (1971). Localities 12and 13 also occur in the Seven Rivers For-mation based on the mapping of Kelley

Chaves County (Locality 6) and followedthat report with a description of pseudocu-bic quartz crystals from Artesia in EddyCounty (Tarr and Lonsdale, 1929). Theterm “Pecos Diamonds” appears to havebeen first mentioned in print by Tarr andLonsdale (1929), where they note that thecrystals were described by that name bylocal collectors. Other names ascribed tothe crystals include “Indian diamonds”and “Pecos valley diamonds,” the latterterm favored by collectors today. Practicaluses for these objects are mainly decorativewith present day uses confined to lapidaryand jewelry. There is no evidence for theiruse, decorative or otherwise, by pre-Euro-pean people.

Initial descriptions of euhedral authi-genic quartz crystals noted the rarity ofthese minerals in evaporite sequences(Tarr, 1929). However, subsequent workhas shown that euhedral quartz crystalsare relatively common in ancient shallowmarine carbonate and evaporite sequences(Folk, 1952; Grimm, 1962; Wilson, 1966;Zenger, 1976; Ulmer-Scholle et al., 1993).They are found throughout the Phanero-zoic and exist in rocks as old as Proterozoic(Grimm, 1962). Other famous occurrencesof authigenic quartz include Herkimer dia-monds hosted by Cambrian dolomites inNew York (Zenger, 1976). Large authigenicquartz crystals have been described inyoung Pleistocene carbonate-evaporitesediments in the Arabian Gulf (Chafetzand Zhang, 1998). One of the most com-prehensive studies of worldwide occur-rences of quartz crystals in evaporites waspublished by Grimm (1962). He noted over150 localities that displayed similar geo-logic and depositional characteristics.

Personal collecting trips by the authorsmore precisely define the geological set-tings of the localities of Tarr (1929) and Tarrand Lonsdale (1929) in addition to docu-menting 10 other in situ occurrences alongthe Pecos River valley. These new localitieshighlight areas where authigenic quartz,dolomite, and/or aragonite crystals are rel-atively abundant, large, or morphological-ly unique. A discussion of color, crystalshape, and inclusion variations is providedfor each occurrence. Ultimately, we willspeculate on the origin of these mineralsand their significance in sedimentologicalinterpretations.

Pecos diamonds–quartz and dolomite crystals from theSeven Rivers Formation outcrops of

southeastern New MexicoJames L. Albright* and Virgil W. Lueth, New Mexico Bureau of Geology and Mineral Resources,

New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801

*Author deceased

64 NEW MEXICO GEOLOGY August 2003, Volume 25, Number 3

FIGURE 1—Location map illustrating the distribution of the Seven Riversand Yates Formations in southeastern New Mexico. Numbers refer toPecos diamond localities discussed in the text and presented in the appen-

dix. Outcrop segments that contain Pecos valley diamonds are identifiedwith arrows. Tectonic elements adapted from Kelley (1971).

August 2003, Volume 25, Number 3 NEW MEXICO GEOLOGY 65

(1972) on the Fort Sumner sheet. We havenot been able to document any occurrencesof Pecos valley diamonds in the Yates For-mation during our study.

Outcrop segmentsBoth tectonic and geomorphic featuresalong the Pecos valley control outcrop dis-tribution of the Seven Rivers Formation(Fig. 1). Pecos diamonds occur sporadical-ly within particular segments of an out-crop belt that is almost continuous. Theseoutcrop segments, and gaps that separatethem, are caused by specific tectonic andgeomorphic controls that were imposedafter Pecos valley diamond development.Descriptions of Pecos diamond localitieswithin specific outcrop segments are pre-sented in the appendix.

Seven Rivers segmentThe Seven Rivers segment starts at thedolomite-gypsum transition near DarkCanyon north to the McMillan escarpment.The southernmost documented occurrenceof Pecos diamonds was mentioned byDake et al. (1938). They report, “at SevenRivers, small doubly terminated crystalsare found, averaging half an inch in length,which have a uniform red-brown color,and are quite perfect. The larger crystalsfrom the same locality averaging 11⁄2 inchesin length are of a dirty brown color withfaces as bright and perfect as the smallerones...these crystals sometimes assume acubical aspect.” The original Seven Riverstownsite is now 11⁄2 mi south-southwest ofthe present village along the transitionzone from dolomite to gypsum facies. Wehave not been able to confirm the presenceof Pecos diamonds at Dake’s locality norhave subsequent studies in the area (e.g.,Sarg, 1981). The segment is terminated bya 71⁄2-mi gap in the outcrop near LakeMcMillan caused by the presence of theFourmile Draw syncline (Kelley, 1971). Thedownwarping of the syncline and subse-quent Quaternary alluvial fill from a mul-titude of streams that drain the SevenRivers embayment cover the outcrop.

Artesia segmentNorth of the Fourmile Draw syncline, theSeven Rivers Formation reappears on theeast side of the Pecos River as the Artesiaoutcrop segment (Fig. 1). This outcrop seg-ment, exposed by the Artesia–Lovingtonarch, is 17 mi long by approximately 3 miwide. The northern margin of this segmentis truncated in the vicinity of the K-M faultand covered by an embayment of alluviumdeposited by drainages on both sides ofthe Pecos River. Tarr and Lonsdale (1929)published their early work on the south-ernmost occurrence of Pecos diamondsthat we can document. Most Pecos valleydiamond occurrences are limited to theupper benches of small bluffs on the eastside of the Pecos River. Excellent exposures

Features of the authigenic quartz crystals

The authigenic quartz crystals from eachPecos valley locality are distinctive enoughas to habit, size, color, and inclusions thatthey can be grouped into suites. Somesuites are traceable for several kilometers,whereas others are restricted to a fewsquare meters. Some localities contain spe-cific forms and colors, whereas others maycontain a diverse range.

SizeCrystals in the New Mexico Bureau ofGeology and Mineral Resources MineralMuseum range from microscopic to a max-imum of 6.5 cm (~2.5 inches) along the caxis. Median length for perfect crystalforms is approximately 2.5 cm (~1 inch);those larger tend to be distorted. Thelargest single crystals found thus far comefrom Locality 13, and the largest clustersare from Locality 3.

ColorPecos diamonds take on a wide range ofcolors (Fig. 2). Perfectly transparent crys-tals are usually less than 4 mm (~1⁄8 inch)long. Larger crystals take on the color ofthe gypsum matrix, usually with a slightincrease in intensity. Occasionally a bleach-ing of the host gypsum adjacent to thequartz crystals is observed. Color bands inthe host rocks, present as laminations oralong fracture joints, commonly cross theincluded quartz crystals without interrup-tion. Opaque crystals are milky white,light to dark gray, red, pink, yellow,orange, light to dark hematite red tobrown, and light to nearly black magenta.Translucent crystals tend to be white,white with pink or orange streaks, or lightto medium honey brown. Nearly transpar-ent crystals from Locality 7 contain cloudygypsum inclusions along with greenish-black material possibly sapropel or hydro-carbon. Some crystals show color zonation.Very large prismatic crystals from Locality12 are variegated creamy gray green withpink points.

Strikingly similar authigenic quartzcrystals are common in the Triassic Keupergypsiferous facies of Spain, where they areknown as “Jacintos de Compostela”– liter-ally, Hyacinths from Compostela, an allu-

of matrix pieces can be found on the mar-gins of drainages that dissect the bluffs.

Roswell segmentNorth of the K-M fault at the mouth of theRio Felix, the Seven Rivers Formationreappears in the Roswell outcrop segmenteast of the Pecos River (Fig. 1). The Roswellsegment is continuous over a north-southdistance of 47 mi with an outcrop widthvarying from 1⁄6 to 31⁄2 mi. The segment dis-appears in the north in the vicinity of theterminus of the Six Mile Buckle of Kelley(1971). Pecos diamond occurrences tend tobe confined to the top of the bluffs in thissegment except along the Pecos River cutbank at Locality 4.

Dunnahoo Hills segmentWest of the Pecos, between Roswell andAcme, a triangular-shaped outcrop is pres-ent in the Dunnahoo Hills (Fig. 1). Noauthigenic quartz or dolomite has beenfound in this segment. The DunnahooHills segment is surrounded by Quater-nary terrace and alluvium deposits andnot defined by tectonic elements, in con-trast with the southern segments. The lackof Pecos valley diamonds in this segmentmay be due to the fact that this segmentonly exposes the lower portions of theSeven Rivers Formation.

Dunlap segmentNorth of Dunnahoo Hills and west of thePecos River, the Dunlap segment of theSeven Rivers Formation forms an irregularfan-shaped outcrop covering over 165 mi2

(Fig. 1). No tectonic elements, as definedby Kelley (1971), are apparent in this broadsegment. Kelley (1971, 1972) noted anabundance of Pecos diamonds in the upperportions of the Seven Rivers Formationwithin this area especially south of ArroyoYeso (Localities 8–12). The majority ofPecos diamond occurrences are foundwithin this outcrop segment, particularlyover broad areas in the southern part. Thenorthernmost occurrence of Pecos dia-monds is west of El Morro Mesa in De BacaCounty (Locality 13). The Seven RiversFormation thins to the north (Kelley, 1972),and Pecos valley diamond occurrencesdecrease in that direction.

Salado Draw segmentThe northernmost occurrence of the SevenRivers Formation is confined to thedrainage valley of Salado Creek at the DeBaca and Guadalupe County line. Kelley(1972) notes that the Seven Rivers, alongwith the Yates Formation, pinches outbeneath the Santa Rosa Sandstone underthe pediment cap of Guadalupe Mesa. Noauthigenic quartz or dolomite occurrencesare known from this segment.

FIGURE 2—An example of color variation ofPecos Valley diamonds from Locality 9.


sion to red-orange precious stones fromthat locality popular during the MiddleAges (Febrel, 1963; Rios, 1963). A compari-son of Pecos diamonds from diverse local-ities cannot be distinguished from theSpanish Jacintos insofar as size, color,form, and inclusions.

Chaves (1896) observed that the SpanishJacintos turned gray on heating and sug-gested that the pigments were in partorganic. This heating experiment wasrepeated on representative Pecos valleydiamonds by Abraham Rosenzweig (at theUniversity of New Mexico) by raising thetemperature in an electric oven to 450° Cand maintaining the temperature for 12 hrs.All samples exhibited loss of color, with theleast change in the hematite red varieties(Fig. 3). Loss of luster occurred primarilyfrom fracturing of the crystal faces follow-ing decrepitation of fluid, hydrocarbon, orhydrous mineral inclusions.

InclusionsIn addition to color, many Pecos valley dia-monds contain discrete inclusions of other

Crystal formsOne of the distinguishing features of Pecosvalley diamonds when compared withother occurrences of authigenic quartz isthe great variation in crystal forms (Fig. 6).The vast majority of quartz crystals are typ-ically hexagonal prisms (Figs. 5, 6B) termi-nated on both ends by positive (r) and neg-ative (z) rhombs (Grimm, 1962; Nis-senbaum, 1967; Chafetz and Zhang, 1998).Tarr (1929) reported a sequential develop-ment of crystals from Acme (Locality 1).Based on size and morphology, he statedthat initially the quartz precipitated as apseudocube (r), afterwards the quartzoid (r+ z) and, finally, the doubly terminatedprism (r + z + m) (Figs. 6 B–D). Unequivo-cal development of any other crystal formsof quartz, although observed elsewhere inthe Seven Rivers Formation in our study,was not observed from specimens in theTarr (1929) study area around Acme. Abasis for size and sequential developmentis rendered false at other localities, howev-er. Some of the largest crystals found arepseudocube specimens (as long as 6 cm[~2.5 inches] along the c axis) at Locality 13in association with large authigenicdolomite crystals.

Prismatic forms. The most commonmegascopic crystal habit in Pecos valleydiamonds is the regular prism (m) pointedat both ends by hexagonal pyramidsformed by equal, or near equal, develop-ment of both the (r) and (z) rhombs (Fig. 5).Grimm (1962) measured 1,000 authigenicquartz crystals that were associated withevaporite deposits from around the world(including the Pecos valley) and found thatthe axial ratios range from 1.5 to 3.0 in themajority of cases, the shortest being 1.1and the most acicular being 5.5. Common-ly the (r) rhomb is relatively large, eventhough the prism (m) faces are equal ornearly so. Most of the (r) faces have abright luster, whereas the (z) faces tend tobe dull. A significant portion of the pris-matic crystals have prism faces that arealternately wide and narrow; thus, in crosssection, the prism zone appears as if trigo-nal prisms are present (Figs. 7 and 6E–plan

minerals. Most common are includedgrains of gypsum in the outer portions ofsome crystals. Nissenbaum (1967) notedabundant anhydrite inclusions in Pecosvalley diamonds and authigenic quartzcrystals contained in evaporite clasts fromIsrael. The anhydrite inclusions are orient-ed along growth planes and are preferen-tially found in the cores of the crystals butabsent on the rims. Anhydrite is notablyabsent in the surrounding evaporite inboth the Pecos valley and Israel occur-rences. Kelley (1971) noted gypsumpseudomorphs after anhydrite in placeswithin the Seven Rivers Formation, how-ever. Large (up to 3 mm, typically 1 mm)rounded, green-black inclusions are rarelynoted in some crystals and may be oforganic origin, although they do not fluo-resce under UV light. These dark inclu-sions are always restricted to the outer-most portions, and some intersect the sur-face of the crystals (Fig. 4).

Crystal surface featuresMegascopic surface features include varia-tions in reflectivity, growth lines, negativecrystal pits, crystal mold impressions, andlinear depressions. Tarr (1929) noted thatthe prismatic faces, when present, are typ-ically rough, whereas the rhombohedronfaces tend to be smooth (Fig. 5). Evenamong the rhombohedron faces, Tarr andLonsdale (1929) noted in pseudocubic vari-eties that the negative rhomb (z) tends tobe dull compared to the positive rhomb (r).When present, growth lines on the prismfaces (m) tend to be subdued and broadcompared with most common quartz.Negative crystal pits are common on prismfaces and locally attain large sizes (7 mm[~1⁄4 inch] on a 5-cm [~2-inch] crystal).These pits may be casts of dissolveddolomite or other evaporite minerals andrepresent mold impressions. Linear de-pressions are typically zones of crystal-growth overlap.

FIGURE 3—Color changes in Pecos valley dia-monds after heating at 450°C. All samples illus-trated as pairs with the heated sample on theleft. Sample pairs A and B from Locality 2, Cfrom Locality 12, and D from Locality 11. Theupper left sample is 1 cm long.

FIGURE 4—Dark inclusions of organic materialobserved in some specimens. Note the quartzcrystal clusters illustrating the tendency forsubsidiary growth on the prism faces of thequartz crystal. Illustrated examples from Local-ity 3. The lower left crystal is 2 cm long.

FIGURE 5—Prismatic forms of Pecos diamondsshowing rough prism faces (m) and smoothrhombohedron faces (r and z), even on second-ary growths. Note the left and center crystalsalso show rough (z) faces. In contrast, both (r)and (z) rhombohedron faces on the crystal onthe right are smooth. Quartz crystals illustratedare from Locality 11. The left crystal is 1.7 cmlong.

FIGURE 7—Quartz crystals displaying partialdevelopment of a pseudotrigonal bipyramidhabit from Locality 1. The crystal on the left is 2cm long.


Pseudotrigonal Pyramids

FIGURE 6—Crystal diagrams of the various forms of Pecos valley diamonds noted in the study area. Diagram modifiedfrom quartz crystal incremental growth concepts of Grimm (1962).


view). The slanted (r) and (z) faces are alsoequally wide and narrow, forming match-ing trigonal pyramids at each end. Tabularcrystals flattened parallel with a pair ofcoplanar prism faces (m) are rare. Only onesuch tabular Japan-Law twin has beenfound at Locality 12; however, normal pris-matic Japan-Law twins are fairly commonat Locality 11.

Equant forms. Equant pseudocubichabit results when the faces of (r) aredeveloped to the exclusion, or near exclu-sion, of both (z) and (m). Because the inter-face angle is 85°46’, these crystals appearcubic to the unaided eye. Vestigial devel-opments of (z) and/or (m) are nearlyalways present. Locality 1, first describedby Tarr and Lonsdale (1929), yieldspseudocubic crystals as great as 1 cm (~3⁄8inch) in size. Pseudocubes as long as 2.5 cm(~1 inch) on an edge also occur at Locality13 (Fig. 8).

Equal or near equal development of (r)and (z) to the exclusion or near exclusionof (m), simulates a quartzoid habit, whichis more characteristic of high-temperature

rhombohedra (r) and (z) are bright andsmooth. This is especially true when theaxial ratio is greater than three. At Locality1, tapered prismatic crystals of this type, aslong as 3.5 cm (13⁄8 inches) with axial ratiosaveraging 3.5, also give the illusion ofbeing bent or twisted along the c axis (Fig.11).

Clusters of quartz crystals are some-times observed, especially at Localities 2and 3. Interestingly, these clusters are com-posed of one large core crystal with small-er crystals growing from the (m) facesalmost exclusively (Fig. 4). These smallercrystals tend to grow perpendicular to theprism (m) face. These subsidiary crystalsradiate from the (m) faces parallel to thebedding planes within the host gypsum, afeature also noted in authigenic aragonitecrystals found in the Grayburg–QueenFormation stratigraphically lower in thesection at Locality 13. It is important tonote, however, authigenic quartz is onlyfound with dolomite and never observedwith aragonite.

Features of the authigenic dolomite crystals

Euhedral, authigenic dolomite crystals alsooccur in the Seven Rivers Formation (Fig.12). Sparse, light to medium honey-yellowcrystals have been found at Locality 3. AtLocality 4, medium to dark honey-browncrystals as great as 2 cm (~ 3⁄4 inch) in sizeoccur in and weathered from massivewhite gypsum slump blocks. These crystalsdo not withstand weathering and are diffi-cult to free from matrix. Nevertheless, bothfine matrix specimens and loose crystalsfrom this locality are found in museumsaround the world. Small (5 mm), scarce,transparent to translucent, euhedraldolomite crystals occur in white gypsumwith abundant medium to dark honey-brown prismatic quartz crystals that aver-age 2.5 cm (~1 inch) in length at Locality 12.

quartz known as beta quartz (Frondel,1962). This form is best thought of asmatching (r) and (z) faces at the ends of avery narrow prism zone. Localities 2 and 6,and especially at the latter, contain abun-dant examples of this form (Fig. 9). Theobvious low-temperature environmentrequired by the mineral assemblage in thePecos valley suggests a high-temperatureorigin for beta quartz forms is notrequired.

Pseudotrigonal bipyramids (Figs. 10, 6E)at Localities 1 and 13 are the result of therare over development of (r) and diminu-tion of (z), to the exclusion or near exclu-sion of the prism faces (m). These are alsothe localities with abundant pseudocubictypes and may represent modification ofpreviously formed pseudocubes (Albrightand Krachow, 1958) in a manner similar tothat described by Tarr (1929).

Distorted crystals. The prism (m) facesare not always completely developed andmay be rough and pitted, even when the

FIGURE 8—Equant pseudocubic quartz crystalsfrom Locality 13, placed at various orientations.The large crystal on the top is 2.5 cm across.

FIGURE 9—Pecos diamonds exhibiting thequartzoid and pseudo-octahedral habits fromvarious localities. Top crystal group represents acommon twinning habit in beta quartz. Crystalbottom center is a pseudo-octahedral type. Noteinitiation of prism face growth on left and rightquartzoid crystals. The crystal on the lower leftis 2 cm long.

FIGURE 10—Trigonal prism form of Pecos dia-monds from Locality 1. Note the color zonationin the upper portion of the crystal. Maximumdimension is 2.2 cm.

FIGURE 11—“Bent or twisted” appearingquartz crystals from Locality 1. These crystalstend to be more mottled than typical Pecos val-ley diamonds. Largest crystal is 4 cm.

FIGURE 12—Examples of loose authigenicdolomite from the study area. Maximum lengthof the largest crystal is 2 cm.

FIGURE 13—Crystal drawings of the variationsin authigenic dolomite crystal morphology fromthe study area.


The geometry of the dolomite crystals isformed by combinations of the positiverhombohedron {4041} truncated by posi-tive and negative basal pinacoids spaced atspecific axial ratios (Fig. 13). Crystal Types1 through 7 are found at Locality 3, includ-ing one specimen with hemimorphic trun-cations by Types 7 and 8 pinacoids. Thesecrystals average less than 1 cm (3⁄8 inch) inlength. Types 4 and 5 dolomite forms occurat Locality 4. Locality 12 contains Types 1through 5, and they average 2.5 cm (~1inch). No Type 9 dolomite forms have beenrecognized in the study area. Where gyp-sum matrix pieces are available, carefulexamination of vugs occupied by Pecosvalley diamonds in a couple of locations (2and 9) suggests that the space may havebeen originally a dolomite rhomb (Fig. 14).

Known as “las Teruelitas” in Spain, blackpseudo-octahedral Type 4 dolomite crys-tals were first described by D. AmalioMaestra in 1845 from a similar geologic set-ting. At the type locality (Barranco de Sola-bral, northeast of Teruel in the province ofthe same name) the Teruelitas occur withblack Jacintos de Compostela in a gray toblack Keuper gypsum (Muñoz and Piñero,1951). Chemical analyses of the Teruelitasshow them to be calcian-dolomite. Theblack color results from a small iron andmanganese content. Rogers (1949) firstreported on the similarities of Pecos valleydolomite to Spanish Teruelitas.

DiscussionDuring his study of over 150 authigenicoccurrences of quartz in evaporites,Grimm (1962) noted features that werecommon to all localities: 1) presence ofsaline facies; 2) evidence of euxinic envi-ronments; and 3) evidence of petroleummigration and entrapment. We will pro-vide more information on these features inaddition to specifying some of the detailsof the depositional environment, timing ofthe quartz formation, and speculate on the

probably a function of the scattered natureof salinas or salt pans that served as catch-ments for meteoric water and perhaps fine-grained wind-blown sand and silt. Thesilty units could serve as a potential sourcefor silica although other workers havecited a biogenic source of silica, mainlyfrom sponge spicules (Ulmer-Scholle et al.,1993; Chafetz and Zhang, 1998).

Alternatively, the distribution of thePecos valley diamonds may representzones of diagenetic alteration or fluidmigration in the deep subsurface. Fluid orhydrocarbon migration may have beenconfined to the upper portions of theSeven Rivers Formation, hence the absenceof Pecos valley diamonds in the lower por-tions. The presence of anhydrite inclusionsmay be indicative of deeper burial, and thesilica could be derived from diageneticalteration of clays. The gypsum-rich outerzones observed in some Pecos valley dia-monds may be linked to subsequent upliftdiagenesis and the conversion of anhydriteto gypsum during final quartz growth.

The presence of dolomite and absence ofaragonite are important indicators for thepresence of Pecos valley diamonds. Inevaporite units that underlie the SevenRivers Formation (e.g., the Grayburg–Queen Formation) large and euhedralaragonites are fairly common and quartz isabsent. Chafetz and Zhang (1998) also notean absence of quartz in aragonite and low-magnesium calcite units that overlie thequartz-bearing dolomites in the Gulf ofArabia. They suggest the aragonite low-Mg units were deposited in a marine envi-ronment, more similar to the Grayburg–Queen Formation. This relationship sug-gests that the Seven Rivers Formation mayhave undergone dolomitization and thatthe Pecos valley diamonds formed duringor shortly after this process. The formationof the quartz in this environment wouldnot require deep burial and is probablycharacteristic in portions of the sabkhaenvironment. Nissenbaum (1967) alsorejected a deep burial replacement originfor Pecos valley diamonds based on thepresence of growth lines and zonal anhy-drite found in the quartz crystals. Hebelieved the quartz was formed duringprimary anhydrite precipitation onsupratidal salt flats, consistent with thesabkha depositional model.

However, the very large size of theauthigenic dolomite and quartz crystalsare not common in low-temperature, sedi-mentary environments. Large crystal sizesin these minerals are more characteristic ofthe hydrothermal environment and mayindicate deep burial and formation duringdiagenesis at higher temperatures.

The role of organic matterSignificant changes in oxidation and pHare required for the formation of dolomiteand later formation of quartz. Stable iso-tope work has identified organic carbon as

processes that may have led to the forma-tion of the Pecos valley diamonds.

A fundamental question that remainsunanswered is the timing of Pecos valleydiamond precipitation. The presence ofauthigenic quartz in deeply buried evapor-ites and carbonates is well known (e.g.,Ulmer-Scholle et al., 1993). However, therecent discovery of modern megaquartz indolomite in the Arabian Gulf (Chafetz andZhang, 1998) reveals the possibility ofearly diagenetic formation near the sur-face. The features exhibited by the Pecosvalley diamonds and their host rocks havemuch in common with those described byother workers as characteristic of bothnear-surface and deep environments.These competing modes of formation willbe discussed with regard to the possibleorigin of these fascinating quartz anddolomite crystals.

Depositional environment Previous sedimentological studies of thePermian Seven Rivers Formation inferredthe depositional environment to be similarto modern sabkha environments present inthe Arabian Gulf today (Kendall, 1969; Till,1978; Ward et al., 1986; Warren, 1989). Thedistribution of authigenic dolomite andquartz crystals appears to be related to aspecific depositional environment withinthe Seven Rivers Formation. The crystalsare not distributed uniformly throughoutthe evaporitic sequence stratigraphicallyor across the study area. The crystals tendto be concentrated near the top of the for-mation (Kelley, 1971) and are only sporad-ically distributed within the entire outcroparea. In general, their distribution patternis typically circular to elongate.

The distribution patterns of Pecos valleydiamonds, and their tendency to be mostabundant stratigraphically adjacent to thinshale units, suggests they were confined tosubenvironments of the sabkha, most like-ly shallow salinas or salt pans. The spottydistribution of Pecos valley diamonds is

FIGURE 14—Authigenic dolomite (A.) and Pecos valley diamond (B.) in matrix from Locali-ty 1 an 11 respectively. The dolomite crystal in A. is a Type 4 (Fig. 13), pseudo-octahedralshape. Note the rhombohedral shaped vug in sample B with quartz occupying only part ofthe space. A small rim of gypsum marks the extent of the original crystal that dissolved andleft the vug later partially filled by quartz crystal with a pseudo-trigonal prism form. Bothspecimens are 7 cm in the longest dimension.


involved in the anaerobic bacterial reduc-tion of sulfur to sulfide before chert forma-tion in some chalk units (Clayton, 1986).Similar studies on authigenic quartz inkarst settings (Palmer, 1995) noted animportant contribution by organic carboncompounds in the formation of quartz.Bennett et al. (1988) also identified the abil-ity of organic compounds to dissolve andlater reprecipitate quartz.

Abundant organic matter is observed inpartially aragonitized mats presentlyforming in the Macleod evaporite basin ofAustralia (Logan, 1987), another potentialmodern analog to the Seven Rivers Forma-tion. This material forms a sapropel, a jelly-like ooze composed of algal remains mac-erating and putrefying in an anaerobicenvironment in shallow water. Otherworkers have noted periods of hydrocar-bon migration and associated evaporitesilicification in the Seven Rivers Formationsouth of the study area (Ulmer-Scholle etal., 1993). Regardless of the type of organicmatter, it appears it had an important rolein the reduction of sulfate to sulfide inparts of the study area and may havemobilized silica for later precipitation asPecos valley diamonds.

Dolomite and quartz formationAuthigenic dolomites within the SevenRivers Formation are unusually large andhave a wide variety of morphologies nottypical of sedimentary environments.These crystals are typically dark whencompared to the matrix. This is in contrastto the similar colors exhibited betweenhost rock matrix and quartz crystals. Thisdark coloration may be due to smallamounts of manganese or iron like Spanish“Teruelitas,” although the matrix in thePecos valley is not dark like that in Spain(Muñoz and Piñero, 1951). Alternatively,they may be dark colored because ofhydrocarbon or sulfide mineral inclusionsindicative of reducing conditions duringtheir formation. In contrast, authigenicquartz is typically associated with oxi-dized colors and mineral phases. We havenot observed dolomite and quartz in thesame sample or stratigraphic layer,although they can be found together at aparticular locality. The mutually exclusiveoccurrence within a particular stratigraph-ic horizon may indicate an aspect of eachmineral’s formation that precludes thepresence of the other. Accordingly, wespeculate that the dolomite and quartzformed at different times based on thepresence of rhomb-shaped vugs occupiedby quartz.

Many of the features within the quartzcrystals suggest that they formed by bothopen space precipitation and in situreplacement of gypsum and dolomite.Some of the Pecos valley diamonds arefound in vugs with rhombohedral outlinessimilar in form to the authigenic dolomites(Fig. 14). Larger quartz crystals undoubt-

rocks would be useful in testing the specu-lations presented in the discussion above.Variations in both carbon and oxygen iso-topes should fall within values observedby other workers (e.g., Clayton, 1986;Palmer, 1995) and help identify the typeand role of organic matter in this process.

Detailed mapping of quartz, dolomite,and aragonite occurrences may prove use-ful for delineating different depositionalenvironments within the Seven Rivers For-mation or pathways for diagenetic fluids,depending on the results of fluid inclusionanalysis. The limited distribution of thePecos valley diamonds suggests that theyare unique to particular depositional/dia-genetic environments within fairly monot-onous evaporite units. Detailed petrogra-phy of the evaporites and associated siltyunits may also show evidence of quartzsolubility within the host rocks (e.g., Ben-nett and Siegel, 1987).

AcknowledgmentsThe second author (VWL) would like tothank the Albright family, especially Jim’swidow Carrie and son Jon, for permissionto publish this work with modifications. Inaddition, the manuscript reviews of Drs.Brian Brister, NMBGMR, and Dana Ulmer-Scholle, NMIMT, are gratefully acknowl-edged along with the help and suggestionsfrom the editorial (Jane Love and NancyGilson) and cartography (Leo Gabaldon)staff members of the New Mexico Bureauof Geology and Mineral Resources.

ReferencesAlbright, J. L. and Bauer, R. M., Jr., 1955, Pecos Val-

ley diamonds: Rocks and Minerals, v. 30, nos. 7–8,pp. 346–350.

Albright, J. L. and Krachow, T. 1958, Schwebendgebildete quartzcristalle in New Mexico: DerAufschluss, v. 5, pp. 98–101.

Bennett, P. C., Melcer, M. E., Siegel, D. I., and Has-sett, J. P., 1988, The dissolution of quartz in diluteaqueous solutions of organic acids at 25°C:Geochimica et Cosmochimica Acta, v. 52, pp.1521–1530.

Bennett, P. C. and Siegel, D. I., 1987, Increased solu-bility of quartz in water due to complexing byorganic compounds: Nature, v. 326, no. 6114, pp.684–686.

Chafetz, H .S. and Zhang, J., 1998, Authigenic euhe-dral megaquartz crystals in a Quaternarydolomite: Journal of Sedimentary Research, v. 68,no. 5, pp. 994–1000.

Chaves, 1896, Effect of heating on Jacintos de Com-postela: Am. Soc. Esp. Hist. Nat., v. 25, p. 243.

Clayton, C. J., 1986, The chemical environment offlint formation in Upper Cretaceous chalks; inSieveking, G. deG., and Hart, M. B. (eds.), Thescientific study of flint and chert: CambridgeUniversity Press, pp. 45–54.

Dake, H. C., Fleener, F. L., and Wilson, B. H., 1938,Quartz family minerals—a handbook for themineral collector: McGraw-Hill, 304 pp.

Febrel, T., 1963, Jacintos contenidos en anhyritas:Materales salinos del Suelo Espanol, Apedice 2:Instituto Geologico y Mineros de España, Memo-ria 64.

Folk, R. L., 1952, Petrography and petrology of theLower Ordovician Beekmantown carbonate

edly exceeded the space of the precursorminerals and further engulfed the evapor-ite minerals. Some quartz crystals appearto have grown entirely within the gypsum,especially those with abundant inclusions.If the quartz replaced earlier dolomiteforms, some of the unusual quartz forms(e.g., pseudocubes, etc.) may actually bequartz pseudomorphs after dolomite. Thepresence of quartz in vugs with rhombohe-dral outlines, similar to dolomite, suggeststhe precipitation of quartz at least accom-panied the dissolution of dolomite.

Tarr (1929) suggested hematite as themain coloring agent in the crystals andspeculated that the coloration was inducedfrom the outside of the evaporite unit afterquartz formation. Later the same year, Tarrand Lonsdale (1929) noted that colorationof the rock preceded the formation of thequartz crystals as the color banding in thehost rock was continuous through inter-vening quartz. They speculated that thesource of the color was from adjacent redbeds. Nissenbaum (1967) analyzed bothauthigenic quartz crystals from Israel andPecos valley diamonds to find some crys-tals contained as much as 0.3% Fe2O3. Wespeculate an influx of meteoric water oxi-dized sulfides, creating locally acidicwaters that dissolved the dolomite and ledto the precipitation of quartz. Stable iso-tope work by Chafetz and Zhang (1998)documented periodic episodes of meteoricwater flushing during in the modernmegaquartz occurrence in the ArabianGulf. A similar episode or episodes of oxi-dation would explain the near ubiquitousred coloration seen in many Pecos valleydiamonds. Alternatively, migration of dia-genetic fluids could also lead to changingfluid chemistry that would favor quartzstability over dolomite.

Suggestions for further workThe varied morphology of the quartz crys-tals, especially variations in crystal faceluster and orientation of subsidiary quartzgrowth on (m) faces suggests that uniquecontrols on crystal growth were presentduring quartz precipitation. Surface stud-ies on these crystals may reveal featuresthat lead to a better understanding of bothinternal and external controls on crystalmorphology.

A fluid inclusion study on the dolomitesand quartz would greatly help to constrainthe origin of the quartz crystals. Homoge-nization temperatures and salinities coulddifferentiate between crystals formed nearsurface and at low temperatures (e.g.,Chafetz and Zhang, 1998) and thoseformed during deeper burial and at highertemperatures (e.g., Ulmer-Scholle et al.,1993). Perhaps the Pecos valley diamondshave components that suggest they formedinitially near the surface and grew largerwith diagenesis. Stable isotope studies oforganic materials contained in inclusionswithin the Pecos valley diamonds and host


rocks in the vicinity of State College, Pennsylva-nia: Unpublished Ph.D. dissertation, Pennsylva-nia State University, 366 pp.

Frondel, C., 1962, The system of mineralogy; v. 3,Silica minerals: John Wiley and Sons, 334 pp.

Grimm, W. D., 1962, Idiomorphe quarze als leeit-mineralien fur salinare fazies: Erdöl Kohle, v. 15,pp. 880–887.

Kelley, V. C., 1971, Geology of the Pecos country,southeastern New Mexico: New Mexico StateBureau of Mines and Mineral Resources, Memoir24, 78 pp.

Kelley, V. C., 1972, Geology of the Fort SumnerSheet, New Mexico: New Mexico State Bureau ofMines and Mineral Resources, Bulletin 98, 55 pp.

Kendall, C. G. St. C., 1969, An environmental re-interpretation of the Permian evaporite/carbon-ate shelf sediments of the Guadalupe Mountains:Geological Society of America, Bulletin, v. 80, no.12, pp. 2503–2526.

Logan, B. W., 1987, The Macleod evaporite basin,western Australia—Holocene environments, sed-iments and geological evolution: American Asso-ciation of Petroleum Geologists, Memoir 44, 140pp.

Meinzer, O. E., Renick, B. C., and Bryan, K., 1927,Geology of no. 3 reservoir site of the Carlsbadirrigation project, New Mexico, with respect towater tightness: U.S. Geological Survey, Water-supply Paper 580-A., pp. 1–39.

Muñoz, C., and Piñero, A., 1951, Breve nota sobre

in gypsum from Acme, New Mexico: AmericanMineralogist, v. 14, no. 1, pp. 19–25.

Tarr, W. A. and Lonsdale, J. T., 1929, Pseudocubicquartz crystals from Artesia, New Mexico: Amer-ican Mineralogist, v. 14, no. 2, pp. 50–53.

Till, R., 1978, Arid shorelines and evaporites; inReading, H. G. (ed.), Sedimentary Environmentsand Facies: Elsevier, pp. 178–206.

Ulmer-Scholle, D. S., Scholle, P. A., and Brady, P. V.,1993, Silicification of evaporites in Permian(Guadalupian) back-reef carbonates of theDelaware Basin, west Texas and New Mexico:Journal of Sedimentary Petrology, v. 63, no. 5, pp.955–965.

Ward, R. F., Kendall, C. G. St. C., and Harris, P. M.,1986, Upper Permian (Guadalupian) facies andtheir association with hydrocarbons—PermianBasin, west Texas and New Mexico: AmericanAssociation of Petroleum Geologists, Bulletin, v.70, no. 3 pp. 239–262.

Warren, J. K., 1989, Evaporite sedimentology—importance in hydrocarbon accumulation: Pren-tice Hall, 185 pp.

Wilson, R. C. L., 1966, Silica diagenesis in UpperJurassic limestones of southern England: Journalof Sedimentary Petrology, v. 36, pp. 1036–1049.

Zenger, D. H., 1976, Definition of type Little FallsDolostone (Late Cambrian), east-central NewYork: American Association of Petroleum Geolo-gists, Bulletin, v. 60, pp. 1570–1575.

las teruelitas: Inst. Geo y Minero de España,Notas y Comuus. 25, pp. 3–8.

Nissenbaum, A., 1967, Anhydrite inclusions inidiomorphic quartz in gypsum concretions fromMakhtesh Ramon, Israel: Israel Journal of EarthSciences, v. 16, pp. 30–33.

Palmer, A. N., 1995, Geochemical models for theorigin of macroscopic solution porosity in car-bonate rocks; in Budd, D. A., Saller, A. H., andHarris, P. M. (eds.), Unconformities and porosityin carbonate strata: American Association ofPetroleum Geologists, Memoir 63, pp. 77–101.

Rios, J. M., 1963, Materiales salinos del SueloEspañol: Inst. Geol. y Minero de España, Memo-ria 64 p.

Rogers, A .F., 1949, Dolomite crystals of the Teruelhabit from Lake Arthur, Chaves County, NewMexico (abs.): Geological Society of America,Abstracts with Programs, v. 60, no. 12, p. 1943.

Sarg, J. F., 1981, Petrology of the carbonate-evapor-ite facies transition of the Seven Rivers Formation(Guadalupian, Permian), southeast New Mexico:Journal of Sedimentary Petrology, v. 51, no. 1, pp.73–96.

Tait, D. B., Ahlen, J. L., Gordon, A., Scott, G. L.,Motts, W. S., and Spitler, M. E., 1962, ArtesiaGroup (Upper Permian) of New Mexico and westTexas: American Association of Petroleum Geolo-gists, Bulletin, v. 46, no. 4, pp. 504–517.

Tarr, W. A., 1929, Doubly terminated quartz crystals

James Lofton Albright was born in Kingwood, West Virginia, onDecember 26, 1922, to Charles and Hazel Albright. He developedan interest in minerals at an early age after seeing the amethystcrystals in a new railroad cut near his home. After graduatingfrom high school at age 16, Albright spent a short amount of timeat the University of West Virginia before the hard economic timesof the depression caused him to leave school and seek employ-ment in the naval shipyards in Orange, Texas. There he met hisfuture wife, Carrie Willey, and they were married in June 1942.After spending 3 years in the South Pacific during World War II,Albright returned to Texas and enrolled at the Texas School ofMines, now the University of Texas at El Paso. There he earned aB.S. degree in mining engineering in 1949. In El Paso, Albright wasable to practice his hobby of mineral collecting in earnest, soonamassing an impressive collection with emphasis on specimensfrom New Mexico, Texas, Arizona, and northern Mexico.

After graduation, Albright began a long and varied career in theoil and gas industry as a geologist and geophysicist. He workedfor Pan American Petroleum in Roswell, New Mexico, from 1950until 1959, and then for Pubco Petroleum in Albuquerque until1966. After a short stint with a NASA project at the University ofNew Mexico, Albright and his family moved to Texas where heworked for Petty Geophysical in Houston and San Antonio. In1971, Albright began work as an independent consultant in Hous-ton. He retired to Canyon Lake, Texas, in 1993 where he passedaway in September 2000.

Albright had a life-long passion for minerals and mineral col-lecting. Most of his collection he gathered himself, including alarge collection of Pecos diamonds. He proudly displayed hismost interesting and favorite samples in special glass cabinets athis home. Albright’s minerals are now part of the collection at themineral museum of the New Mexico Bureau of Geology and Min-eral Resources at New Mexico Institute of Mining and Technologyin Socorro. The donation represents one of the most significant inrecent museum history consisting of many singularly unique andhistoric pieces. A review of Stuart Northrop’s book, The Minerals ofNew Mexico, reveals many entries with described occurrencesattributed to James L. Albright—many of them one of a kind. Inhis tradition of sharing mineralogical knowledge, this paper is hislast work, most of it written shortly after retirement.

James Lofton Albright


Locality no. 1Artesia, NM

secs. 19, 30, 31T17S R27E

Spring Lake 71⁄2-min quad.32°48’59”N

104°18’35”W

AppendixLocalities of authigenic quartz and dolomite crystals.

Locality no. 2Artesia, NM

sec. 18 T17S R27ESpring Lake 71⁄2-min quad.

32°49’39”N104°18’35”W

Locality no. 3Lake Arthur, NM

secs. 33, 34 T15S R26EArtesia NE 71⁄2-min quad.

32°56’57”N104°20’06”W

In secs. 25, 26, and 27 T15SR26E the Pecos River makes asharp west-southwest turn for21⁄2 mi around large obsequent

Locality no. 5Roswell, NM

secs. 3, 10, 11, 14T11S R26E

Bitter Lake, Bottomless Lakes,Comanche Spring, and South

Spring 71⁄2-min quads.33°23’45”N

104°22’38”WLocality no. 6

Acme, NMsec. 30 T8S R26E

Acme 71⁄2-min quad.33°35’18”N

104°20’48”W

Locality no. 7Selmen Draw, Chaves County

sec. 4 T7S R24ECoyote Draw, Shannon Draw

and Marley Draw 71⁄2-minquads.

33°44’21”N104°31’34”W

Tarr and Lonsdale’s (1929)paper, as well as the fine crys-tals that can be found here,especially the pseudocubes,have made this locality thedestination of collectors overthe years. With a little workthis locality can still yieldgood examples of authigenicquartz forms, both loose andin matrix.

Locality 2 is separated fromLocality 1 based on a distinc-tive assemblage of attractive,small, medium to dark blood-red crystals that can bescreened from loose silty sandin large numbers. These aremainly equant forms averag-ing 5 mm with rare pseudo-cubes. No bedrock is exposed.

Deeply weathered Seven Ri-vers gypsite high on a topo-graphic rise in the SE1⁄4 sec. 35T16S R26E along the Eddy–Chaves County line containssparse light to medium honey-yellow euhedral dolomitecrystals as large as 2 cm. Theseare combinations of the rhom-bohedron M{4041} truncatedby a pair of basal pinacoidsTypes 1 through 7.

Sparse, poorly developed,brownish prismatic authigenicquartz crystals, as large as 2cm along the c axis, also occurin and weathered from thegypsite.

Locality no. 4Lake Arthur, NM

secs. 26, 35 T15S R26EArtesia NE 71⁄2-min quad.

32°59’20”N104°19’11”W

In the first professional paperpublished on in situ authi-genic quartz crystals in theSeven Rivers Formation, Tarr(1929) describes white to pinkdrussy crystals “...one milesouthwest of Acme along thehighway to Roswell....Thequartz crystals range from .075millimeter to two centimetersin length.”

On Comanche Hill, 10 mi eastof Roswell in the vicinity ofBottomless Lakes State Park,drussy, light to dark hematite-red quartz crystals were for-merly abundant. The drussyfaces are the terminations ofprismatic crystals radiatingabout the center of a singleshort to long prismatic crystal.If short, the radiating clustermay approximate a sphere. Iflong, the drussy area is usual-ly insignificant.

In the 1930s and 1940sdrussy crystals from Coman-che Hill were used to decorate

Abundant, nearly transparent,prismatic quartz crystals, bothloose and in matrix, occur in theSW1⁄4 sec. 34 T6S R24E and SW1⁄4

slump blocks of Seven Riversgypsite. These slumps resultfrom continuing erosion, aug-mented by solution, along thetrace of the K-M fault. Nearriver level, especially in the

Artesia outcrop segmentSample localities 1–4

vicinity of the gaging station,they contain abundant world-famous-euhedral Types 4 and5 pseudo-octahedral dolomitecrystals.

Dunlap outcrop segmentSample localities 7–13

Roswell outcrop segmentSample localities 5 & 6

cast gypsum ashtrays, bookends, etc. for the tourist trade.They are, or have been, so plen-tiful that this type has becomesynonymous with “Pecos dia-monds” in the minds of mostmineralogists.


Locality no. 9Huggins Hill, Chaves County

sec. 36 T5S R24ECottonwood Draw and

Shannon Draw 71⁄2-min quads.33°49’23”N

104°26’18”W

Abundant dark-magenta tonearly black, short to long,stout, doubly terminated pris-matic crystals occur in andweathered from medium- tolight-magenta gypsite in sec. 13T4S R23E south of the aban-doned Old Cavel School. Thesecrystals average 2 cm but maybe as long as 4 cm along the caxis. A very few of these formnormal prismatic Japan-Lawtwins.

Southeast of the abandonedschoolhouse, plentiful hand-some, opaque, medium hema-tite-red prismatic crystals aslong as 3 cm occur loose in thesoil. Approximately 5% of

Locality no. 12Gibbin Ranch

De Baca CountySW1⁄4 sec. 10, T3S R24E

Lovelady Draw 71⁄2-min quad.34°03’05”N

104°24’32”W

Abundant prismatic quartzcrystals as long as 70 mm andpseudocubes as great as 25 mmon an edge occur in and weath-ered from medium- to dark-gray gypsite in sec. 8 T1N R21Eon the Overton Ranch. Thesecrystals are accompanied byscarce pseudotrigonal bipyra-mids as long as 35 mm alongthe c axis that are formed byunequal development of the (r)and (z) rhombohedra and theabsence or near absence of theprism (m) (Albright and Kra-chow, 1958).

The larger prismatic crystalsare generally mottled reddishcreamy gray or white withpink points, whereas the small-er crystals of all types are aboutevenly divided between whiteand light to dark pink.

Sparse pink, orange, red, andwhite prismatic crystals aver-aging 15 mm along the c axisoccur loose and in white topink gypsum matrix in sec. 36T6S R25E.

Plentiful drussy, medium- todark-orange, prismatic crystalsoccur in and weathered fromlight-orange gypsite bluffs onboth sides of Huggins Creek insec. 11 T5S R25E. Average sizeof these colorful crystals is 18mm.

Sparse loose, white and dark-brown, almost black, prismaticcrystals averaging 15 mmalong the c axis have been col-lected in a shallow ravine insec. 36 T5S R25E.

Locality no. 11Old Cavel School, Chaves

Countysecs. 23, 24 T4S R23E

Dunlap Sill and SwallowNest Canyon 71⁄2-min quads.

33°56’43”N104°29’21”W

On the Gibbin Ranch abundantvery good, light to dark honey-brown prismatic quartz crys-tals occur in and weatheredfrom light-gray to tan gypsitein sec. 10, T3S R24E. Thesecrystals contain copious gyp-sum inclusions. Average size is25 mm. Largest crystal foundmeasures 50 mm (Albright andBauer, 1955).

Scarce, small (5 ± mm), trans-lucent, white euhedral dolo-mite crystals Types 1 through 5are commonly embedded inthe gypsum matrix along withthe quartz crystals. These donot weather well and are easilyoverlooked. Very fine matrixspecimens containing bothauthigenic quartz and dolo-mite crystals are easilyobtained.

Locality no. 13Overton RanchDe Baca County

secs. 7, 8 T1N R21EYeso Mesa SE 71⁄2-min quad.

34°18’50”N104°46’11”W

Locality no. 8Shannon Draw, Chaves County

sec. 2 T6S R24ECottonwood Draw, CoyoteDraw and Eightmile Draw

71⁄2-min quads.33°49’10”N

104°26’13”W

Locality no. 10Huggins Draw, Chaves County

sec. 10 T5S R25EDeering Place 71⁄2-min quad.

33°52’45”N104°18’13”W

sec. 3 T7S R24E. These attractivecrystals, averaging 2 cm alongthe c axis, contain cloudy-whiteinclusions of gypsum andgreenish-black material resem-bling sapropel. Large, dry sink-holes in gypsite, comparable insize to those at BottomlessLakes State Park, suggest origi-nal deposition in a salina envi-ronment.

these form normal prismaticJapan-Law twins.

All illustrations in the article and appen-dix with the exception of Figure 1 werecreated by Virgil Lueth.

nmg25n3: pecos diamonds--quartz and dolomite crystals …pecos diamonds–quartz and dolomite...

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