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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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Carbonates(Nesse, Ch. 17, p. 326-339)
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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Carbonates(Nesse, Ch. 17, p. 326-339)
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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Carbonates(Nesse, Ch. 17, p. 326-339)
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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Carbonates(Nesse, Ch. 17, p. 326-339)
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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Carbonates(Nesse, Ch. 17, p. 326-339)
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
Carbonates(Nesse, Ch. 17, p. 326-339)
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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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Sulphates(Nesse, Ch. 17, p. 340-346)
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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Sulphates(Nesse, Ch. 17, p. 340-346)
gypsum:low relief, low dinclined extinction
anhydrite:moderate relief,moderate to high d
parallel extinction
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Sulphates(Nesse, Ch. 17, p. 340-346)
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
Sulphates(Nesse, Ch. 17, p. 340-346)
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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_fluid8/10/2019 3. Carbonates, Phosphates, & Sulfates WS
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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.pdf8/10/2019 3. Carbonates, Phosphates, & Sulfates WS
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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.pdf8/10/2019 3. Carbonates, Phosphates, & Sulfates WS
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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
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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.html8/10/2019 3. Carbonates, Phosphates, & Sulfates WS
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Anhydrite Structure CaSO4
http://upload.wikimedia.org/wikipedia/commons/b/ba/Anhydrite.GIF8/10/2019 3. Carbonates, Phosphates, & Sulfates WS
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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
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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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Tungstates & Molybdates
Wolframite (Fe,Mn)WO4
Scheelite CaWO4
Wulfenite PbMoO4
SG: 7-7.5
SG: ~6
SG: 6.8
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Tungstates & Molybdates
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