3. carbonates, phosphates, & sulfates ws

8/10/2019 3. Carbonates, Phosphates, & Sulfates WS

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Systematic Classificatin of Minerals

Carbonates, Sulfates, and Phosphates


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Classification of the Minerals


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Carbonates(Nesse, Ch. 17, p. 326-339)

photos: mindat.org

calcite dolomite

magnesite

rhodochrosite

aragonite


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diverse group of non-silicate minerals

basic formula: XCO3or XY(CO3)2X , Y = divalent cations (Ca,Mg,Fe,Mn)

4 main carbonate groupsdistinguished based onstructure + composition:

calcite group

dolomite grouparagonite groupOH-bearing group


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Carbonates

Reason for electrostatic valency calculations:

Amount of residual charge indicates relative strength ofbonds with cations, which are reflected in the hardnessof the mineral


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basic building block: [CO3]2-3-fold symmetry underlies typicalrhombohedral (trigonal) structure

of most carbonates

calcite dolomite

[CO3]2-

Ca2+

[CO3]2-Ca2+

Mg2+


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Carbonates

Aragonite(High-P) Orthorhombic

Calcite(Low-P - Hexagonal)

Most are Hexa onal


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Calcite

Calcite Structure


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The structure of calcite is described as a "modified NaCl"structure, but calcite is not cubic. The carbonate groups

stretch the atomic planes and distort the cube into arhombohedron.


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Kalsit(Rhombohedral)

Dolomit(Rhombohedral)

Aragonit(Orthorombik)

Kalsit CaCO3 Dolomite CaMg(CO3)2 Aragonite CaCO3

Magnesit MgCO3 Ankerite Ca(Mg,Fe)(CO3)2 Witherite BaCO3

Siderit FeCO3 Kutnoherite CaMn(CO3)2 Strontianite SrCO3

Rhodochrosite MnCO3 Cerrusite PbCO3

Smithsonite ZnCO3

Kelompok Mineral Karbonat


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Aragonite GroupCarbonate minerals with a single divalent cation of radius > 1.00 . With

increasing radius the species are Aragonite (CaCO3), Strontianite (SrCO3),Cerussite (PbCO3), and Witherite (BaCO3). Aragonite is denser than calcite,and is the high P polymorph. It crystallizes at ambient conditions andpersists metastably for millions of years. The orthorhombic structure isnearly hexagonal with c as the unique axis.


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Dolomite CaMg(CO3)2

Forms during seasonal high tides that flood limestone (calcite) islandswith seawater. Mg++ in the seawater replaces some of the Calcium ions.

Has very distinctive crystals


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distinguishing features(carbonates in general):variable relief in PPL

uniaxial ve

very high birefringence

NB: calcite and dolomite arenotend members in a single

solid solution series


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distinguishing features(calcite vs dolomite):orientation of twinsrelative to cleavage


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Carbonates(Nesse, Ch. 17, p. 326-339)other calcite groupminerals(limited solid solution with calcite)

otherdolomite groupminerals(solid solution with dolomite):ankerite CaFe(CO3)2

kutnahorite CaMn(CO3)2


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aragonite:orthorhombic polymorph of CaCO3

other aragonite groupminerals:witherite BaCO3strontianite SrCO3cerussite PbCO3


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Carbonates(Nesse, Ch. 17, p. 326-339)aragonite:

orthorhombic polymorph of CaCO3

also formed by some organisms(metastable; reverts to calcite

during diaganesis)

stable at high P,low T


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Other CarbonatesAzurite - Cu3(CO3)2(OH)2 (Blue)

Malachite Cu2CO3(OH)2(Green)

Rhodochrosite MnCO3


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Calsite Group


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DolomiteGroup


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Aragonite

Group


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OH-bearing group


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occurrence:dominant constituents of limestones and dolostonesform primary phases in some igneous rockscommon in veins and other secondary assemblagesmarbles and other metcarbonate rocks

use:calcite:essential component of industrial cement;

raw material for lime (CaO) which hasa wide variety of uses; pharmaceuticals;agriculture; neutralising agent; building stone

dolomite:a variety of industrial uses includingagriculture, ceramics, cement, aggregate;mined for Mg in some places



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Borate Groups


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Borates

Kernite Na2B4O6(OH)23H2O

Borax - Na2B4O5(OH)48H2O

Ulexite NaCaB5O6(OH)65H2O

H 2-2.5; SG 1.7

H 3; SG 1.95

H 1-2.5; SG 1.96

Television Rock


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BorateMinerals


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Sulphates(Nesse, Ch. 17, p. 340-346)

photos: mindat.org

gypsumanhydrite

barite

desert rose:intergrown crystals

of gypsum or baritecementing fine sand


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MineralGroupsformed withAnionicComplexes

Carbonates

SulfatesSO

4

--

Phosphates

Silicates

NEXT:

Next time

Today

After Thanksgiving


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The Sulfate Ion has Sulfur in tetrahedral coordination with 4 oxygens.Sulfur, element 16, with 1S2 2S2 2P6 3S2 3P4 electrons, so 6 electrons inthe outer shell of the neutral atom. These 6 electrons shared with theOxygens,1S2 2S2 2P4,

leaving the Sulfate Ion SO4with a charge of -2, SO4--

Two double bonds and two single bonds

Notice BOTH S and O have 6 valence electrons

Pp 60-61


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Figure 17.1 b Sulfate IonSO4-- We consider theS valence +6 (as if ionic)O valence always -2

Amount of residual charge(charge not neutralized)indicates relative strengthavailable for bonds withcations, reflected in the

hardness of the mineral

Pp 60 61Electronegativities: S2.4, O 3.5Difference 1.1, only 25% ionicK&D Fig 3.21 So mostly covalent, i.e.electrons spend almost as much

time near Sulfur

Residual charge on eachOxygen = -1/2

x 4 Oxygens = -2


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Sulfates: Metals + Sulfate Ion

The Sulfate Ion has Sulfur in tetrahedral coordination with 4 Oxygens.Sulfur, element 16, with 1S2 2S2 2P6 3S2 3P4 electrons, so 6 electrons inthe outer shell of the neutral atom. These 6 electrons shared with the

Oxygens, leaving the Sulfate Ion SO4with a charge of -2, SO4 --

Again: The Sulfate Ion: strong covalent bonds, acts as a unit.


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minerals containing [SO4]2-forms tetrahedral groupslinked by divalent cations

gypsum CaSO4.2H2Oanhydrite CaSO4barite BaSO4

gypsum:strongly bonded CaSO4layers alternate with H2O layers

anhydrite:[SO4]2-groups linked by Ca in 8-fold co-ordination


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Sulphate Group


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gypsum:low relief, low dinclined extinction

anhydrite:moderate relief,moderate to high d

parallel extinction


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barite:official IMA name is spelled barytemoderate relief, low d

parallel extinction

[SO4]2-

groups linked byBa2+in 12-fold co-ordination


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occurrence:gypsum, anhydrite: common in marine evaporite deposits

anhydrite can precipitate directly or form bydehydration of gypsum

barite: common in hydrothermal deposits but can also formin terrestrial evaporites

use:gypsum: important construction material (gyprock)

also used in cement, agricultureanhydrite: agriculture, cementbarite: main ore mineral for Ba;

also used in drilling mud, pharmaceuticals, glass,ceramics, and a variety of other industrial uses



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Common SulfatesHYDROUS ANHYDROUS

Gypsum CaSO42H2O

Barite BaSO4 and similar

Anhydrite CaSO4

H: 3-3.5

SG: 4.5

H: 3-3.5SG: 2.9

H: 2SG: 2.32


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Sulfate Ion Radius = ~1.49 Angstroms

Cation Val. Cation Radii (Angstroms)

Barium Ba+2 1.68 [12] Barite

Strontium Sr+2

1.48 [12] CelestiteLead Pb+2 1.57 [12] Anglesite

In all three, cation in 12-fold coordination wOxygens O

e.g. in Barite, each BaO12group is bonded to sevenindividual (SO4)-2tetrahedra

Solid solutions limited within these species. Why?

S in SO4 TETRAHEDRAL [4] Coordination w Oxygen

These three very difficult to distinguish in hand specimens

XSO4


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Barite Group Structure

Cation of Barium Ba++, of Strontium Sr++, of Lead Pb++ surrounded by 12 oxygens


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Barite

BaSO4 Orthorhombic 2/m 2/m 2/m H 3 - 3.5 G 4.5

Gangue in hydrothermal veins, w/ Ag,Pb, Cu. Often near hot springs. Use for heavy drilling mud

Absorbs x-rays in medical diagnosticstudies of the digestive tract.

B it B SO
http://en.wikipedia.org/wiki/Drilling_fluidhttp://en.wikipedia.org/wiki/Bariumhttp://en.wikipedia.org/wiki/Bariumhttp://en.wikipedia.org/wiki/Bariumhttp://en.wikipedia.org/wiki/Bariumhttp://en.wikipedia.org/wiki/Drilling_fluid


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All photos courtesy ofJohn Betts

Barite BaSO4Orthorhombic 2/m 2/m 2/m

Mined locally Hopewell

http://rruff.geo.ari

d /d lib/
http://rruff.geo.arizona.edu/doclib/cm/vol15/CM15_522.pdfhttp://rruff.geo.arizona.edu/doclib/cm/vol15/CM15_522.pdfhttp://rruff.geo.arizona.edu/doclib/cm/vol15/CM15_522.pdfhttp://rruff.geo.arizona.edu/doclib/cm/vol15/CM15_522.pdf


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Barite BaSO4

zona.edu/doclib/

cm/vol15/CM15_

522.pdf
http://rruff.geo.arizona.edu/doclib/cm/vol15/CM15_522.pdfhttp://rruff.geo.arizona.edu/doclib/cm/vol15/CM15_522.pdfhttp://rruff.geo.arizona.edu/doclib/cm/vol15/CM15_522.pdfhttp://rruff.geo.arizona.edu/doclib/cm/vol15/CM15_522.pdfhttp://rruff.geo.arizona.edu/doclib/cm/vol15/CM15_522.pdfhttp://rruff.geo.arizona.edu/doclib/cm/vol15/CM15_522.pdf


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Other Sulfates in the Barite Group

Celestite SrSO4Orthorhombic

2/m 2/m 2/mCleavage {001} perfect,{210} goodH 3-3.5

G 3.95-3.97

Also called Celestine

Often light sky blue in color


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Other Sulfates in the Barite Group

Anglesite PbSO4Orthorhombic

2/m 2/m 2/mCleavage {001} good,{210} imperfectH 3

G 6.2-6.4

Much greater SG


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Gypsum Hydrous CaSO4 CaSO4.

2H2O Monoclinic 2/m {010} perfect H 2, G 2.3

Luster vitreous to pearly

Varieties Selenite clear simple 2/m

Satin Spar fibousAlabaster fine-grained massiveSource for drywall (gypsum board,

sheetrock) and Plaster of Paris


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Gypsum (continued)

Pictures courtesy John Betts and mindat.org

Monoclinic2/m
http://www.mindat.org/photo-31058.htmlhttp://www.mindat.org/photo-72186.html


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Gypsum Structure

From Klein and Hurlburt Manual of Mineralogy 20th Edition.

Looking down along c-axis. Note perfect (010) cleavages. `


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Anhydrite

CaSO4 Orthorhombic 2/m 2/m 2/m Xtals rare {010} {001} {100} tabular

H 3-3.5, G ~3 Luster vitreous to pearly on cleavage

Used in making H2SO4


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Anhydrite

Photos by Martins da Pedra courtesy Mindat.org
http://www.mindat.org/photo-119959.htmlhttp://www.mindat.org/photo-116441.htmlhttp://www.mindat.org/photo-1844.htmlhttp://www.mindat.org/photo-42242.html


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Anhydrite Structure CaSO4
http://upload.wikimedia.org/wikipedia/commons/b/ba/Anhydrite.GIF


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CaSO4.2 H2O

CaSO4.1/2 H2O

CaSO4

Gypsum

Hemihydrate

Anhydrite

Anhydrite may be formed by the dehydration of Gypsum

95oC

68oC

Evaporite Minerals


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Evaporite Minerals

Most of Evaporites are Halides and Sulfates

Volume of water

50% calcite precipitates,gypsum at 20% volume,halite at at 10% volume


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Evaporites Precipitate when concentration in water at To

reaches their saturation limit. Minerals precipitate in reverse order of their

solubilities,

Order of precipitation from sea water is: Calcite (first, but very little volume) Gypsum (CaSO4-2H2O) and/or Anhydrite

(CaSO4). To dependant. Halite (i.e. common salt, NaCl)

Potassium and magnesium salts KCl, KNO3,MgSO47H2O

Discussion: Dead Sea, PlayasMessinian Crisis

Conditions for precipitation


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Conditions for precipitation

Seawater influx into confined basins New rift, shallow bay, playa, isolated

basin in dry climate.

Freshwater evaporates away Lower freshwater influx than

evaporates

Saturated solution exists

Playas (cont'd)


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Playas (cont d) A Playa in Death Valley, California

Evaporite crust


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Swimmers in hypersaline Dead Sea

Evaporite deposits indicate high aridity index.


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Salt Domes: evaporites rise

Mainly NaCl Halite as evaporitedeposits, very low density.

Rising columns deflect sediments Forms hydrocarbon traps that make

petroleum affordable Gulf Coast Jurassic rifting confined

basin

G lf C t ti t l i


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Gulf Coast continental margin

Rising Salt Domes
http://www.slackpacker.com/domesandbasins.html


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Salt Dome lease351-17Gulf Of MexicoCourtesy ShellExploration,HoustonUsed with

Permission


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GEOL 751 Lecture 6:

Cementation & Diagnesis

Influx of

Magnesium

Rich

ContinentalGround

Waters

Influx ofsea water

Evaporation

of mixed

Waters

1. Aragonite

2. Gypsum

3. Anhydrite

4. Dolomite

5. Haliteaccumulate

in this order


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Phosphate Minerals


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Phosphates

Apatite Ca5(PO4)3(F,Cl,OH) prismatic hexagonal crystals common in igneous rocks and

hydrothermal deposits- variable colors the deceiver


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Other Common Phosphates

Monazite (Ce,La,Y,Th)PO4Ore mineral for Rare Earth ElementsUseful mineral in U-Pb and Th age dating

Wavellite Al3(PO4)2(OH)35H2ORadiating globular aggregates

Turquoise CuAl6(PO4)4(OH)85H2O


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Chromate: Crocoite

PbCrO4Monoclinic 2/m.Commonly in prismatic crystals,vertically striatedb=102o33

Cleavage {110} perfectH 2.5 3G 5.9-6.1Luster AdamantineColor bright red to orange- redStreak orange-yellow


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Arsenate


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Vanadates


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Tungstates & Molybdates

T & M l bd


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Wolframite (Fe,Mn)WO4

Scheelite CaWO4

Wulfenite PbMoO4

SG: 7-7.5

SG: ~6

SG: 6.8


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3. carbonates, phosphates, & sulfates ws

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