PARAGENESIS OF THE MINERAL ASSEMBLAGE ATCRESTMORE, RIVERSIDE COUNTY, CALIFORNIA

JonN W. Dalv, CaliJornia Institute oJ Technology,Posadena, California.

INTRODUCTION

For more than twenty years the Creslmore locality has excitedthe interest of mineralogists. This interest was first aroused whenspecimens of blue calcite with monticellite and xanthophyllite weresent to A. S. Eakle. The first publication appeared in 19141 andsince then numerous papers have been published on the miner-alogy of Crestmore by A. S. Eakle, W. F. Foshag, A. F. Rogers,and others.

Crestmore is situated on the extreme eastern lobe of the JurupaMountains about three miles west of Riverside, California. The

Jurupa Mountains are an east-west range roughty eight miles longand three miles wide which parallels the front of the San GabrielMountains.

The cement plant, l imestone quarries, and mine of the River-side Cement Company are located at Crestmore. Quarrying opera-tions were started some seventeen years ago. The rocks were atfirst used as road metal, burned lirne for sugar refining, and forthe manufacture of cement. With the increased demand for cementthe quarrying operations were given or-er entirely to that purpose.At the present t ime the material is obtained by underground min-i.g.

PURPOSE AND METHOD OF INVESTIGATION

Although much work has been done on the mineralogy of theIimestones and associated rocks at Crestmore, never before hasthe geology been mapped and the mineralogy studied in its relationto the geology of the district for the purpose of determining theparagenesis of the minerals and their petrological associations.With this purpose in mind as a major objective, the work was con-ducted and resulted in the following related units:

1. Detailed geologic study of the Crestmore quarries and theeastern portion of the Jurupa Mountains.

l Eakle, A. S., and Rogers, A. F., Wilkeite, A New Mineral of the Apatite Groupand Okenite, Its Alteration Product: Am. four. Sci , vol. 27 , pp. 262-267, 1914.

JOURNAL MINERALOGICAL SOCIETY OF AMERICA

2. Economic study of a typical Southern California l imestone

deposit.3. Collection and determination of a large amount of mineralogi-

cal material by chemical analysis and optical methods.4. Organization of this material into a catalogue of mineralogical

associations.Unfortunately some of the rare minerals described from this

locality were entirely removed during the quarrying operations.Hence in preparing a catalogue of the mineral species it wasnecessary to take some of the data from the l iterature and in these

cases the relationships and associations could not be precisely

determined.The map of the Crestmore quarries was made on the scale of

I" :100' on a topographic map kindly f urnished by the Riverside

Cement Company. The hil ls to the west of the quarries weremapped on a portion of the U.S.G.S. San Bernardino Quadrangle,originally on the scale of 1":1 mile photographically enlarged to

1 inch equals one-half mile. Locations were determined by means

of a Brunton compass and a l ight plane table.

ACKNOWLEDGMENTS

The writer wishes to thank the officials of the Riverside Cement

Company, Mr. John Treanor, Mr. G. A. Beckett, and Mr. Earl

MacDonald, for their permission to make a geologic map of the

quarries. Messrs. Thomas Mullan and C. A. Robotham of the

same organization were very helpful. Much credit is due Dr. Ren6

Engel, of the California Institute of Technology, under whose

direction this work was conducted, for the help he has given.

GEOLOGY

The geologic study of the district and the economic aspects of

the Crestmore l imestones wil l be the subject of another paper.

However, it is entirely within the scope of the present paper and

will add materially to its value to give here a brief resum6 of the

geology. A geologic and topographic map of the Crestmore quarries

is shown on Plate 1.

Stratigraphy.

The oldest rocks of the Jurupa Mountains form a thick series of

recrystallized sedimentaries for which the name, Jurupa Series, is

proposed. The stratigraphically lower part of the section' consist-

//,F

GEOLOGIC MAPOF TTIE

CRESTMORE QUARRIESRIVERSIDE CO., CALIF

F'{PIJI{iATION

AUATERNARY ALLWIUM

rd-"]DUNE SANDS

INTRUSTVE FOCXSPRE -CBETACMUS

mPEGMAIM DITGS

ATZ MONZONITE POFHY}T'

ni$F_qGMN@I]RJE

)ffil/o$#{c-"ffi|i$s.,E N f f i

ffiITE CArcITE Bu CMMSKT BLUE QIARRY UMESrcNE

74KXC}ID{o QURRY CTJAMXT

ffirc QUART{/ U}DSTONE

CONIACT ROCK

NW'ASSOCIATED WIfr Q,}rcNZONITE P.

SYMBOIJCoNTACT, cm-lMru-.-+-

DIP AND aRXE /

642 THE AMERICAN MINERALOGIST

ing of undifferentiated quartzites, schists and gneisses with small

l imestone lenses, wil l be referred to as the Undifferentiated Com-plex. Lying on this complex, with the same attitude and possibly

conformably, are the l imestones which are exploited for cement

manufacture. These were differentiated on the large scale map of

the Crestmore quarries (Plate 1) into the following units: (1) The

lower, Chino Quarry limestone, (2) Overlying qtartzite and schist

beds, called the Chino Quarry quartzite, (3) The upper, or Sky

Blue Quarry l imestone. Granodiorite and quartz monzonite in-

trusions separate these lower members from the upper l imestone.

In mapping this last unit an effort was made to trace the l imits of

the development of the blue calcite. Because of the uncertain

nature of the outcrops this distribution could not be carried

through in detail but is indicated in a general way on the map

(Plate 1) .

T he U ndifer entiated C omPlex.

These rocks are best exposed in the hil ls about two miles north-

west of Crestmore. The stratigraphic units are tabulated below in

descending order:

1700 ft. thin bedded quartzite interstratihed with fissile mica schist.

850 ft. coarse bedded quartzitic schists.

1050 ft. biotite gneiss in part schistose.

100 ft. hard, thick bedded, quartzite in part schistose.

3700 ft. +

Granodiorite cuts off the base of the section and intrudes parts of

it thus making it impossible to determine the true thickness of the

section.

The Chino Quarry Limestone.

This l imestone, the best exposure of which is in the Chinoquarry, is lvhite, medium to thin bedded, and medium to coarselygranular. Graphitic beds are found throughout the section but are

more common near the base. Another conspicuous rock type is the

calcite-brucite rock, or predazzite. Pseudo-isometric crystals of

brucite occur in beds of medium grained, white l imestone. Rogers2

2 Rogers, A. F., An American Occurrence of Periclase and its Bearing on the

Origin and History of Calcite-Brucite Rocks: Am. Jour. Sci., vol.46' pp. 582-586,

1918. Periclase from Crestmore near Riverside, California, with a List of Minerals

from this Locality: Arn Mineral., vol. 14, pp.462469,1929.

JOURNAL MINERALOGICAL SOCIETY OF A]/IERICA 6+3

has shown that these brucite crystals are pseudomorphs afterpericlase, remnants of which can sti l l be found enclosed in thebrucite. Associated minerals are chondrodite, spinel, magnetiteand wilkeite.

The base of this l imestone has been cut off by granodiorite sothat the true section cannot be ascertained. The maximum exposedthickness is of the order of 470 feet. The total would undoubtedlybe considerably greater.

The Chino Quarry Quartzite.

The structural relations between the Chino Quarry quaftziteand the Chino Quarry l imestone is not precise. They are in partseparated by a sil l- l ike intrusion of granodiorite. Where their con-tact is exposed they are apparently conformable, but the quartzitehas a shallower dip than the underlying limestone. The top of thequartzite has been cut ofi by intrusions of granodiorite and qnartzmonzonite porphyry, except at the eastern end where it appearsto be unconformably overlain by limestone, but the exposures arepoor and this relation is not certain. The examination of diamonddrill cores and the underground workings proves that the down-ward extension of these rocks is severed by intrusions about twohundred feet below the surface.

A total thickness of at least 75 feet is exposed. The formationconsists of interstratified, thin bedded, quartzite and fissile micaschists.

The Sky Blue Quaruy Limestone.

Except for the development of the blue calcite and the moreintense metamorphism near some of the quartz monzonite dikes,this formation is lithologically similar to the Chino Quarry lime-stone. There is no evidence to show that the original sediments ofthese two units differed appreciably in chemical composition. This

study has proven that any differences are directly related to thevarying degrees of metamorphism to which each limestone has

been subjected.Igneous intrusions have separated the Sky Blue Quarry lime-

stone from the underlying Chino Quarry quartzite so that theirrelations can only be inferred. The attitude of the formationsdiffers appreciably. This may be due to distortion during intrusion,

or possibly the intrusion followed a line of previous structural

weakness. i.e.. an unconformitv or a fault.

6M THE AMERICAN MINERALOGIST

Alluvium covers the top of the section but a thickness of over500 feet is exposed in the quarries.

Other Outcrops.

In the Jensen quarry to the west and in several other parts ofthe area studied, outcrops of l imestone are found. They are l itho-logically similar to the l imestones described above but their struc-tural relations are so obscure that their further discussion in thispaper is not warranted.

Age and. Suggested Correlation of the Jurupa Series.

Because of the isolated position of this range and the lack offossils, correlation had to be based on lithologic similarity. On thisbasis, the Undifferentiated Complex is thought to be the equiva-lent of the Arrastre quartzite and the l imestones equivalent to theFurnace limestone described by Vaughan3 from the San BernardinoMountains. Vaughan considered the Arrastre qtaftzite as lowerCambrian and the Furnace limestone as upper Cambrian andOrdovician. Later work by Woodford and Harrissa proves thatat least the upper portion of the Furnace limestone is Mississippian(?). Since it is apparent that the age of similar rocks is not preciselyknown, the Jurupa Series has been assigned to the Paleozoic (?)era without attempting to relate it to any particular period orperiods.

Quoternary Alluoium.

Undifferentiated dune sands, river sands, and fan deposits aregrouped under this unit.

fcNrous Rocrs

In this region five distinct but related plutonic rock types arefound. Apparently these types are the result of differentiation froma parent magma and range from hypersthene quartz diorite topegmatites.

H y p er sthene Quartz Diorite.

This oldest and most basic rock outcrops on the hil ls southwest

3 \raughan, F. E., Geology of the San Bernardino Mountains North of SanGorgonio Pzss'. Bull. Dept. Geol., tlniv. CaliJ., vol. 13, pp. 319412, 1922.

a Woodford, A. O., and Harriss, R. S., Geology of Blackhawk Canyon, San Ber-nardino Mountains, California: Bull,. Dept. Geol., Unio. CaliJ., vol. 17, pp. 265-304. 1928.

JOURNAI. MINERALOGICAL SOCIETY OF AMERICA 645

of Crestmore. A microscopic determination shows the following:

The texture is holocrystalline, medium grained, hypidiomorphic,inequigranular. The femic minerals are represented by slightlypleochroic hypersthene, hornblende, in part uralit ic, and biotite.The feldspar is a basic andesine and shows slight zoning. Undula-tory quartz was the last mineral to crystallize. Pyrite and apatiteare the accessories. Near the periphery the rock shows texturaland mineralogical differences. The texture is porphyritic. Thephenocrysts are labradorite and the feldspar of the ground massis andesine. Quartz is less abundant. These variations can bereadily explained by the different rates of cooling that would ob-

tain at the center and at the periphery of the mass.

Granodiorite.

It forms the bulk of the intrusive rocks in the area mapped. Oneof its most characteristic features is the presence of basic inclusions.These are roughly egg shaped, from two inches to one foot long,

and are, to some extent, oriented with their long axes parallel toeach other. The texture and the mineralogical constituents of theseinclusions show their affinity with the peripheral phase of thehypersthene quartz diorite from which they were probably tornby the intruding granodiorite.

A holocrystall ine, coarse to medium grained, hypidiomorphic,inequigranular texture is characteristic of the granodiorite. Most

of the femic material is pleochroic hornblende. Chlorit ized biotiteis present in lesser amounts. Sericit ized oligoclase with subordinate

amounts of orthoclase constitute the feldspathic elements. The

abundant qtartz shows undulatory extinction. The accessories areapatite, zircon and hematite.

Quartz M onzonite Por phyry.

Numerous intrusions of this rock cut the l imestones in the Crest-more quarries and it is to solutions emanating from these intrusions

that most of the rare minerals owe their genesis. The texture isholocrystall ine porphyrit ic, hypidiomorphic, f ine-grained, inequi-granular. The feldspars are orthoclase and oligoclase both asphenocrysts and as constituents of the ground mass. They show

alteration to calcite and sericite. Abundant qtartz occurs in part

in micropegmatit ic intergrowth with the orthoclase. Scatteredgrains and aggregates of pale green augite constitute the femic

THE AMERICAN MINERALOGIST

material. Pleochroic grains and aggregates of titanite are common.Apatite and pyrite are the accessories.

The peripheries of the larger dikes and of many of the smallerones exhibit marked endomorphic effects resulting from theassimilation of foreign material and from more rapid cooling. In ageneral way these effects are:

(1) Frequent development of porphyrit ic texture.(2) An increase in the abundance of the ferromagnesium con-

stituents and a change in their character. In this case we havediopside, diallage, augite, and grossularite.

(3) An increase in the amount and basicity of the plagioclase.( ) In many cases a complete disappearance of quartz.

Granite Porphyry.

The granite porphyry outcrop, in the western portion of the

Jurupa Mountains, is too far removed from the quarries to meritclose consideration in this paper, but its occurrence is interestingin its relation to the igneous sequence.

The texture is holocrystalline, medium grained, porphyritic,hypidiomorphic, inequigranular. Microcline, oligoclase, orthoclase,qlrartz, biotite, rutile, magnetite and apatite are the mineralsrepresented.

Pegmatite Dikes.

In the literature on the Crestmore quarries the statement thatthe pegmatite dikes are abundant and commonly traverse thelimestone is often made. The writer's observations are at variancewith this statement for very few of these dikes are seen and neverin the limestone. It is possible, however, that the dikes mentionedin the literature were small and were removed during quarryingoperations.

An abundance of pegmatite dikes occurs in the hills adjacent tothe quarries. They vary in width from less than an inch to as muchas twenty-five feet and some of them can be traced for miles. Manyof these dikes show banding. The outer bands are made up oflayers, one-half to one inch thick, composed of graphic intergrowthsof quartz and albite. The inner zone, having a width of about one-tenth the total thickness of the dike, is composed of extremelycoarse feldspar and quartz with the occasional development ofblack tourmaline and biotite. The composition of the feldsparvaries between albite and microcline.

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 6+7

Age and Sequence of the Intrusite Rocks.

Intrusions of Jurassic age occur in the Santa Ana Mountains

and in the Julian district. Vaughans correlates the Cactus granite

of the San Bernardino Mountains with the Jurassic granites of the

Sierra Nevada but mentions an earlier intrusion which may belong

to the Paleozoic. Since there is a possibil i ty that the JurupaMountain intrusives might be earlier than Jurassic their age is

designated merely as pre-Cretaceous.The sequence of intrusions has followed the order: hypersthene

quartz diorite, granodiorite, qvartz monzonite porphyry, granite

porphyry and pegmatite dikes. Their order and spatial relation-

ship suggest dif ierentiation from the same parent magma and

that the intrusions followed closelY in point of t ime.

Cowracr Rocxs

Three distinct types of contact rockquartz monzonite porphyry intrusions.the order of their importance.

Garnet Contact Rock.

The face of the Commercial Rock quarry and the crest of Sky

Blue Hil l is made up almost entirely of this material. The greatest

proportion of the rock is badly fractured massive grossularite'

Other minerals, in the order of their importance, are diopside,

diallage, calcite, wollastonite, augite and scapolite.

V esuaianite C ontact Rock.

At the corner of Lone Star, Wet Weather and Commercial Rock

quarries a contact rock consisting chiefly of vesuvianite and calcite

is developed. The proportions of these minerals vary greatly' In

places the rock is nearly all vesuvianite, quite massive and glassy'

at others the calcite and vesuvianite are approximately in equal

amounts. The other extreme is found when the mass is almost all

calcite with only a few grains of vesuvianite embedded in it ' The

calcite occurs as a soft, white mass of aggregates of extremely fine

needles and some very small rhombohedrons. These forms prob-

ably represent rapid crystallization from a supersaturated solu-

tion. Diopside, garnet and wollastonite are the minerals commonly

associated with this rock.

5 Vaughan, F.8., Op. cit., 1922.

have been formed by the

These are l i s ted be low in

648 THE AMERICAN MINERAL)GIST

In several places in the Wet Weather quarry this assemblage isfound definitely confined to certain beds, thus indicating that theinitial character of the limestone strata may have been one of thegoverning factors in its origin. It is interesting to note that in thiscase the calcite is quite coarsely crystalline.

Quartz and Garnet Contoct Rock.

This rock is composed wholly of granular, vitreous qrartz, andgrossularite crystals and grains. ft is found close to a small quartzmonzonite porphyry dike near the outcrop of the Chino Quarryquartzite in the saddle north of the Chino quarry. This associationindicates its derivation from an impure l ime bearing sandstone.

MINERALOGY

It is impossible in this paper to include a complete catalogue ofthe minerals. Hence, the following descriptions are limited to newoccurrences or to controversial subjects to which the author hasnew data to add.

Following this section the minerals are alphabetically tabulatedin a manner which shows their petrologic distribution, their rela-tive abundance and, to a large extent, their associations. For moredetailed information the reader is referred to the abundant litera-ture on this locality.

Sulphides: Eakleo states that the sulphides are associated withthe pegmatite intrusives. The author has not found this to be thecase. Where the association has been seen the sulphides are con-centrated near the qnartz monzonite porphyry. No sulphides arefound as accessories in the pegmatites, but they are present assuch in the quartz monzonite porphyry. fn the author's opinionsolutions from the quartz monzonite deposited the sulphidemineralization found in the quarries.

M onticellite: This mineral has been described by Eakle7 from theblue calcite and later by Til leys from the contact rock. Eakle sug-gested that the monticellite results from the metamorphism of thebrucite limestone, while the diopside and vesuvianite were formedduring the metamorphism of the pure beds. Thus he accounts for

6 Eakle, A. S., Minerals Associated with Crystalline Linestone at Crestmore,Riverside County, California: Bull Dept. Geol., Univ. Cali.J., vol.l0, pp. 327-360,1917.

7 op. cit., 19t7.8 Tilley, C. E., On a Custerite,bearing Contact Rock from Calilornia: GeoI.

Magozine, pp. 371-372, 1928.

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 649

the scarcity of monticellite and xanthophyllite. fn an earlier paperEaklee attributed the formation of these minerals to solution actionaccompanying the qtartz monzonite porphyry intrusion. Thewriter's observations confirm the earlier statement by Eakle, forotherwise it would imply that the brucite l imestone is l imited inextent, while, on the contrary, it is quite common.

Diallage: Diallage is found in the endomorphic phases of theqrartz monzonite porphyry, and in the garnetiferous contact rock.

Orthoclase: According to Eaklelo orthoclase forms the largerportion of the pegmatite dikes. In the samples examined by theauthor no orthoclase was found in the pegmatites, only albite andmicrocline. It does occur, however, in the granodiorite, the graniteporphyry and the qvartz monzonite porphyry.

Oligoclase: This is the plagioclase feldspar of the granodioriteand also occurs in the enclaves in the granodiorite. It is a con-stituent mineral of the quartz monzonite porphyry, the hypers-thene quartz diorite, the granite porphyry and the UndifferentiatedComplex.

Labradorite: This has been described by Eaklell as one of theconstituents of the granodiorite, along with oligoclase. No evidencehas been found for two generations of plagioclase. The plagioclaseis entirely oligoclase. Labradorite occurs as phenocrysts in thehypersthene quartz diorite and in some of the basic enclaves inthe granodiorite. A few grains were found in the UndifierentiatedComplex and the Chino Quarry quartzite.

Bytownite-Anorthite: Crystals of plagioclase of the bytownite-anorthite type were found in a small cavity at the border of oneof the small qvartz monzonite porphyry dikes in the lower Chinoquarry. They were associated with pyrite, chalcopyrite andbornite.

Scapolite: A grey white scapolite with violet streaks has beenmentioned by Eakle. The material collected by the author is whiteand composed of small radiating aggregates of extremely fineneedles, so fine that to the unaided eye the material appears almostmassive. It occurs in the contact rock associated with wollastonite,calcite, diopside, and grossularite, surrounding these minerals andf i l l ing spaces between them. The indices, a:1.567 +.005, e :1.548

eEakle,A.S. ,Xanthophyl l i te inCrystal l ineLimestone:. /aar.Wosh Acad.Sci ' ,vol . 6, pp. 332-335, 1916.

10 op. cit., l9l7.t1 Op. cit , 1917.

650 TH E AM ERICAN MINERALOGIST

+.005, measured on one sample would indicate, according toWinchell'sl2 diagram marialite 600/6, meionite 400/6, or the speciesdipyr i te . Another sample gave values co:1.504*.005, e:1.550+.005, which corresponds to the values of a mixture oI 40/emarialite, and 60/6 meionite, or the species mizzonite. This is anuncommon form of crysta"llization for scapolite. The fine crystallin-ity would suggest extremely rapid growth of crystals by rapidcooling of a supersaturated solution. Ifowever, the associatedminerals are very coarse, so that this condition does not apply toall of them

Clinozoisite: A pale, transparent to translucent, greenish greyvariety occurs in shattered crystals and grains in a small contactmass associated with one of the smaller quartz monzonite porphyrydikes in the Chino quarry. The associated minerals are garnet andcalcite. This undoubtedly results from the hydrothermal actionof solutions from the qtarLz monzonite porphyry on the l imestone

Epi.dote: Small black crystals, up to three mill imeters in length,were found disseminated in the white Chino l imestone and asso-ciated with the deweylite and chrysotile, near a dike ol qtartzmonzonite porphyry. A green epidote is abundant in some of thepegmatites as already noted by Eakle.

Xanthophyllite: This mineral was first described from this lo-cality by Eaklels as disseminated in the blue calcite and associatedwith monticell i te. The above occurrence was not found but smallcrystals and flakes were found in a locally developed, coarselycrystall ine green calcite in the Chino Quarry l imestone that wasassociated with a small dike oI quartz monzonite porphyry.

Chrysotile ond. Deweylile.' A massive green mineral was found inthe white calcite of the Chino Quarry l imestone in East Chinoquarry, a few feet from a small quartz monzonite dike. An analysiswas made by Mr. Thomas Mullan of the Riverside Cement Com-pany and the following results were obtained:

SiOz(Fe, Al)z OaCaOMgoHrOCOz

40.88

5 . 9 13 7 . 5 21 2 . o o2 . 5 0

i00 .0812 Wincheil, A. N , The Properties of Scapolite.: Am. Mineral, vol. 9, pp. 108-

t r2 ,1924.13 Op. cit., 7977.

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 651

Calcite grains could be seen in the material so CaCOr and(Fe, Al)rOa were discarded and the other figures recalculated on thebasis of 100 per cent.

per cent mol-numbers ratios

sio, 45 .20 7 5 3M g O , . . 4 1 . 5 0 1 0 4 4H,O. 13 .30 .74 3

This gives the formula 3HzO 4MgO.3SiOr, or H6MgaSirOrg, whichdoes not correspond with any of the known hydrous magnesium-sil icate minerals. Grains of the material show indices as follows:A min imum of 1.528*.005, the maximum is 1.555+.005. I f th iswere one mineral the birefringence would be 0.027, which is muchtoo great in comparison with the observed birefringence. Thus it

is thought that this represents a mixture of chrysotile and dewey-lite. A mixture of these minerals in the proportion 68.8/e deweyliteand 3L2/6 chrysoti le would give an analysis corresponding to the

above one. A thin section of the material proved that two minerals

were present.Rogersla describes deweylite replacing hydromagnesite in the

calcite-brucite rock, and regards it as a supergene mineral. In viewof its present relation to the quartz monzonite porphyry dike it

seems that the genesis of these sil icales can be assigned to the

action of solutions emanating from this dike on previously formed

minerals (epidote or diopside as suggested by their nearby oc-currence) and thus in this case their origin would be hypogene'

Sepiolite: A white, fibrous mineral was found filling small veinsin the calcite near the occurrence of the chrysotile and deweylite.The material is composed of finely interlocked fibers with the fibers

oriented parallel to the vein walls. An analysis by Mr. Mullangave the following results:

Sio:(Fe, Al)zOaCaOMso.HzOCOz

Total

44.380 . 8 2

1 1 . 9 020.2413.099 . 4 9

g 'g 'n

The nature of the material made it impossible to free it, for

analysis, from small grains of calcite so that CaCOa and (Fe, Al)zOr

were removed and the figures recalculated to 100 per cent.

11 0b. cit.. l9l8

TH E AMERICAN MINERALOGIST

per centSioz 57.00MeO 26 00HrO. 17 00

mol-number ratios

. . 9 5 . . 3.645 2.945 3

The above ratios correspond to the formula: 2MgO.3SiO, 3HrO.Tlris probably represents a mineral between sepiolite and para-sepiolite, but since the water content of sepiolite is variable themineral has been called sepiolite. Optical properties are:Iy'-:1.510+.005, extinction parallel to the fibers, biaxial negative, bi-refringence low. It is unattacked by HCl. 1y'- for sepiolite is 1.52and for parasepiolite 1.506. This mineral has intermediate opticalproperties as well as composition.

The proximity of this occurrence to the chrysoti le and deweylitesuggests that the sepiolite represents an alteration product of theseminerals.

In the following table (Table 1) the minerals are listed in alpha-betical order. At the right, in vertical columns, are entered thenames of the predominate rock types of this locality. The petro-logic distribution and to some extent the relative frequency ofoccurrence and the relative importance in a rock is indicated, foreach mineral, by an appropriate letter. This gives a general con-ception of the mineral associations.

The purpose of this table is to summarize, in a general way,much of the data on the minerals of this locality. For more detailedinformation on any mineral the reader is referred to a paper byRogersls in which a complete bibliography is given.

PARAGENESIS

The present record of the metamorphic history of the l imestonesshows no efiect of the intrusion of hypersthene quartz diorite, thefirst member in the suite of intrusions which has altered theserocks. The spatial relations show that this intrusion was too faraway to have had any effect other than recrystall ization and frac-turing resulting from heat and stresses produced during the in-jection of the magma.

The flow structure, so often found in the granodiorite near thecontact with the sedimentaries, and the coarse crystall inity of therock indicates that at the time of intrusion it was very viscous,

15 Rogers, A. F., Periclase from Crestmore, near Riverside, California, with aList of Minerals from this Locality: Am. Minerol., vol. 14, pp. 12,462-469,1929.

IOURNAL MINERALOGICAL SOCIETY OF AMERICA 653

and cooled slowly, l ikely under great pressure. Its contribution to

the metamorphism of the l imestone has been: (1) Recrystall izationand Iurther fracturing of the l imestone. (2) The reduction of thecarbonaceous material to graphite. (3) With a few exceptions theformation of the contact metamorphic minerals which are formedmostly under high pressure and temperature and without abundantmineralizers. This was accomplished in the following manner:(a) dissociation of magnesium carbonate to periclase; (b) by re-action in the impure limestone with the formation of spinel, mag-netite, grossularite, wollastonite and diopside; (c) probably at a

Iater stage chondrodite, wilkeite and phlogopite were formed byhydrous emanations from the magma containing phosphate, sul-phate and halides. The hydration of the periclase to brucite tookplace, in part, during the cooling of this intrusion.

The contact metamorphic effects of the quartz monzonite por-phyry were both endomorphic and exomorphic, but it is with thelatter efiects that we are principally concerned here, as the othershave already been briefly discussed. As a consequence of this in-trusion the l imestones were further fractured and further re-crystall ized, especially near the borders of the dikes, unti l in someplaces the previous structures were eliminated. Chemical changesresulting from heat, pressure and the action of mineralizers weremore general and more complex than those of the granodiorite.The most important of these changes from the standpoint of mag-nitude is the development of the garnetiferous contact rock. Thisdevelopment is particularly intense above the dikes where, wemay assume, the action of the mineralizers would be concentrated.The total destruction in this mass of all previous structures andits coarse crystall inity indicates a complete reaction involving thismaterial and slow cooling during subsequent recrystall izationunder rather uniform pressure. Thus by the solvent action on animpure l imestone of the sil icate solutions accompanying the quartzmonzonite porphyry intrusion the formation of such minerals asgrossularite, augite, diopside, diallage, wollastonite, scapolite,monticell i te and bytownite-anorthite has been effected.

The manner in which the vesuvianite-calcite type of rock isconfined to the outer margins of the contact mass suggests thatits development was largely determined by physio-chemical rela-tions in which a lower temperature and favorable concentrationsin AlzOa and SiOr were important factors.

654 THE AMERICAN MINERALOGIST

Tanr,n 1A-AccBssonv Mrxlnlr,; C-Colrlrox; F-Fnnqunxr; M-CoNsrrrutxr MrNonar,; R-RlnE

MrNEner,s Occunnrmcn Rrlr.qnxs

o€o

(,E

tr

o

N

cd

R

N

c

o!o

an

O

AlbiteAndesineAnglesite -ApatiteApophylliteAragoniteArsenopyriteAugite. .Axinite.AzuriteBiotiteBorni te.Bruci te.Bytownite-AnorthiteCalciteCentrallasiteCerusiteCusterite.Chalcedony.ChalcociteChalcopyriteChloriteChondroditeChrysotileClinochlore.ClinozoisiteCrestmoreiteDatolite.DeweyliteDiallageDiopside.EpidoteFoshagiteGalenaGehleniteGraphiteGrossulariteGreenockiteHematiteHornblendeHydromagnesiteHyperstheneJurupaite

Mnf

A

Alteration of galena

In wollastonite near contaclIn veinlets

Associated with garnetOccurs as stains

In cavities near contactAlteration of periclaseIn cavities near contact

Replaces quartzAlteration of galena

In cavities near contactIn cavities near contactAlteration of biotiteDisseminated i n pr edazziteSmall masses near monz. dike

Small masses near contactDisseminated in blue calciteMassiveSmall masses nearmonz. dike

In veins cutting vesuvianite

Associated with merwiniteDisseminated

Coating sphaleriteAlteration of iron minerals

Alteration of brucite

In cavities in limestone

R

R I RC

M F M

RRRR

R

RRR

RRC(l

R

C

MM

R

MR

CMM

tvl

N

d

a b

F

C C

JOURNAL MINERALOGICAL SOCIETV OF AMERICA 655

Tesrn 1 (Contintr,ed)

MrNrnar,s Occunnpxcr RBrrelrs

KaoliniteLaumontiteLabradoriteLimoniteMagnetileMalachiteMerwiniteMonticelliteMicroclineMuscovite(Jkenite.OligoclaseOpalOrthoclasePericiasePhlogopitePlazolitePrehnitePyriteQuattzRiversideiteRutileSepiolite

SericiteSphaleriteSpinel

TetrahedriteThaumasiteTilleyiteTitaniteTourmalineUraliteVesuvianiteWilkeiteWollastoniteXanthophylliteZircon..

!o

d

M

pi

N

d

FM

a

RM

AM

p]

N

N o

o

a-F

CF

RR

R

R

F

CR

p

R

FRCR

CFR

R

RR

F

R

FM

Alteration of feldsparCoating prehnite

StainsDisseminated in the PredazziteStainsLarge masses in blue calcite

Alteration of apophyllite, wilkeite

Enclosed by brucite

In cavities in feldsparDisserninated in limestone

In veinlets in vesrtvianite

In veinlets in predazzite

DisseminatedAssociated with merwiniteIn veinletsIn veins and coating spurriteAssociated wi th wol laston i l "e

In blue anrl green calcite

THE AMERICAN MI I{ERALOGIST

Similar sil icate solutions operating outside of the garnet and thevesuvianite zones and therefore probably at lower temperatureswere responsible for the formation of the associated rare mineralsmerwinite, gehlenite, and spurrite. The fine granular and theacicular wollastonite were also formed in the outer portion of thecontact zone.

After the crystall ization of the garnet and vesuvianite contactrocks and following the high temperature reactions, but in partcontemporaneous with them, hydrous solutions containing phos-phates, halides and sulphates found easy access into the l imestonesand contact rocks along the bedding planes and numerous frac-tures. This probably represented the latter part of the pneumato-lit ic stage or the early part of the hydrothermal stage. By theiraction on the l imestones and on the previously formed contactrocks they formed various hydrated minerals. It is thought thatfrom reactions of this type minerals such as epidote, clinozoisite,wilkeite, chondrodite and custerite were produced. By furthercooling crestmoreite, riversideite, foshagite, jurupaite and plazolitewere formed. Crestmoreite, riversideite and foshagite are probablyalterations of wilkeite.

Deweylite, chrysoti le and sepiolite developed when the hydro-thermal solutions acted probably on diopside and diallage orepidote of the contact zone. Xanthophyll ite could have beenformed either from preexisting sil icates or from the impure l ime-stone but under the conditions observed in the field it seems moreprobable that it too is an alteration of diopside or a closely relatedmineral. The reaction of the sulphated solutions on the spurriteresulted in thaumasite. Sulphide solutions deposited the sulphideminerals. ft was in this stage of the hydrothermal action that thehydration of the periclase to brucite ended.

The metamorphic action of the pegmatite is similar in manyrespects to that of the quartz monzonite porphyry although notas intense and with the characteristic development of some boro-silicate minerals. The first phase is characterized by the develop-ment in the pegmatite and in small adjacent contact zones of thecommon wollastonite, grossularite and the hydrous sil icate epidote.This was followed shortly by apophyllite, prehnite, and the boro-sil icates, tourmaline, axinite and datolite. During the third stageapophyllite altered to okenite, prehnite to laumontite, and central-lasite replaced quartz. Eakler6 mentions okenite as an alteration

JOURNAL MINERALOGICAL SOCIETY OF AMERICA o.) /

product of wilkeite, but whether this alteration took place duringthe hydrothermal stage related to the quartz motzonite porphyryor during that same stage of the pegmatites is unknown.

Other reactions that have occurred here are entirely supergene.The iron bearing minerals have yielded hematite and limonite,galena has altered to cerrusite and anglesite, the copper mineralsto aztrite and malachite. Circulating waters have depositedsecondary qrartz, chalcedony, opal, secondary calcite and aragon-ite. Rogersl7 described hydromagnesite as a supergene alterationproduct of brucite and deweylite as a supergene alteration ofhydromagnesite.

SUMMARY

In recapitulating the results of thesepoints are emphasized:

invest igat ions the fo l lowing

Pateozoic(?) sandstones, shales and limestones have been in-

truded and recrystallized by a related series of pre-Cretaceousplutonic rocks in the order: hypersthene qrartz diorite, granodi-orite, quartz monzonite porphyry, granite porphyry and pegmatitedikes. Of these only the granodiorite, the qtartz monzonite por-phyry and the pegmatite dikes have been particularly effectivemetamorphic agents.

In the Crestmore quarries the principal effect of the granodioritehas been recrystallization and fusion. The more potent quartz

monzonite developed large masses of contact rocks and most of

the rare minerals found here. The action of the pegmatite has beensimilar but not as intense.

In the following the contact metamorphic minerals are listed

below the rocks to which thev owe their origin:

Cronod.iorite Qtz.Monzoni,tePorphyry

Graphite GrossularitePericlase AugiteSpinel DiopsideMagnetite DiallageGrossularite WollastoniteWollastonite Scapolite

16 Eakle, A. S., a1. cit., 1917. Jurupaite, a New Mineral: Am. M'inerol., vol. 6,pp. 107-109, 1921.

17 Rogers, A. F., An American Occurrence of Periclase and Its Bearing on theOrigin and History of Calcite-Brucite Rocks: Am. Joru. Sca., vol.46' pp. 581-586,1918.

Pegmatites

GrossulariteWollastoniteEpidoteApophyllitePrehniteTourmaline

658 THE AMERIC.I .Y MII 'ER.I LOGIST

Gronodiori,te

DiopsideChondroditeWilkeitePhlogopiteBrucite

Qtz. Monzonite Porphyry

MonticelliteBytownite-AnorthiteVesuvianiteMerwiniteGehleniteSpurriteEpidoteClinozoisiteWilkeiteChondroditeCusteriteRiversideite

CrestmoreiteFoshagite

JurupaitePlazoliteDeweyliteChrysotileSepioliteXanthophylliteThaumasite

SulphidesBrucite

Pegmalites

AxiniteDatolite

OkeniteLaumontiteCentrallasite

ft should be evident from the preceding pages and the abovelists that the reactions which took place during and following theseintrusions were not simple and complete; they were characterizedby their extreme complexity and recurrence. Thus it is that manyminerals are polygenetic, not only in that they have been g.enera.tedby each successive intrusion but they have been formed during thesame intrusion by derivation from different parent minerals dueto variations in concentration, pressure and temperature thatmust have prevailed in a mass of this type and size. Not only ispolygenesis evident but one finds that the same minerals yieldvarious alteration products. For example: wollastonite, a mineralcommon to each intrusion, occurs as four distinct morphictypes (a fact in itself of genetic significance) but as shown byDunhaml8 some of the alteration products of this mineral areti l leyite, gehlenite and vesuvianite. Gehlenite in turn yieldsgrossularite. We know that all of the grossularite is not alteredgehlenite and that all of the vesuvianite did not come from wol-

18 Dunham, K. C., A Note on the Texture of the Crestmore Contact Rocks:Am. Mineral . , vol . 18, pp. 11,474, 1933

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 659

Iastonite. We are fairly certain of the intrusion which these re-actions accompanied but not if they occurred during a later lowtemperature or a recurrent phase of the intrusion. These and manyother questions can be answered only by further work.

The following graphically depicts some of the genetic sequencesas they are known to date.

MgCOr+Periclase-B rucite-HydromagnesiteEpidote and/or Diopside+Chrysotile and Deweylite-SepioliteWollastonite+ Gehlenite- Grossulari te

\esuvianiteTilleyite

Wil keiteq-Crestmoreite-R iversideit eApophyllite>.OkeniteSpurrite+ThaumasitePrehnite+Laumontite

Quartz+Centrallasite

fn studying the literature on Crestmore anent the paragensiseof the minerals occurring there one finds confusing and conflictingstatements. Some authors do not distinguish between the differentcontact zones related to the various intrusions, the phases of eachintrusion and in one case the nature of the injected rock has beenincorrectly determined. In short, the tendency has been to toogreatly simplify the facts and to regard the evidence of specialcases as representative of the whole. If we are to more fully under-stand the contact metamorphic phenomena demonstrated hereit is necessary to take a broader view. It is hoped that this paperwill serve as a step in the right direction.