GY 302: Crystallography & Mineralogy

UNIVERSITY OF SOUTH ALABAMA

Lecture 15: Sulfates and Phosphates

(Class VI and VII Minerals)

Instructor: Dr. Douglas Haywick

Last time (before the test)

Carbonates, Nitrates, Borates 1. Select carbonate minerals

2. Sphalerite and galena (left over sulfides)

Featured mineral association: MVT-ores

(Mississippi Valley-type ores)

Carbonates, Nitrates, Borates

•There are 70 carbonate minerals, over 60 borates and a few nitrates

•All 3 types of minerals involve planar anion groups….

•… with the exception of BO44- which is tetrahedral

•Oxygen atoms are strongly covalently bonded in the anion (especially in CO3

2-), but bonding between the anion and the cation is ionic

Carbonates

Calcite Group (3 2/m): Calcite (CaCO3) Magnesite (MgCO3) Siderite (FeCO3) Rhodochrosite (MnCO3) Smithsonite (ZnCO3) Dolomite Group (3): Dolomite (CaMg(CO3)2) Ankerite (CaFe(CO3)2) Kutnahurite (CaMn(CO3)2) Zincian Dolomite (CaZn(CO3)2)

Carbonates

Calcite Group (3 2/m): Calcite (CaCO3) Magnesite (MgCO3) Siderite (FeCO3) Rhodochrosite (MnCO3) Smithsonite (ZnCO3) Aragonite Group (2/m 2/m 2/m): Aragonite (CaCO3) Witherite (BaCO3) Strontianite (SrCO3) Cerussite (PbCO3)

Aragonite (CaCO3) Crystal: Orthorhombic (pseudo hexagonal) Pt. Group: 2/m 2/m 2/m Habit: euhedral, hexagonal prisms SG: 2.94; H: 3.5-4 L: vitreous; Str: white Col: colourless (pinkish) Clev: poor{010}, {110} Optics: Biaxial - nα= 1.530; nβ= 1.682; nγ= 1.686

Name derivation: From its type location, Aragon in Spain

Carbonate Minerals

MVT-ores Mississippi Valley-type ore

deposits •Named after the type mines in Missouri, Tennessee and other sites in the Mississippi Valley

•Low temperature (epithermal) sedimentary ore deposits

•Primary minerals produced: dolomite (saddle), calcite, fluorite and some old friends….

Today’s Agenda

Sulfates and Phosphates

1. Class VI Minerals: Sulfates, Chromates, Molybdates, Tungstates 2. Class VII Minerals: Phosphates, Arsenates and Vanadates

3. Economics of Class VII minerals

Sulfates etc.

Gypsum (CaSO4·2H2O)

Crystal: Monoclinic Pt. Group: 2/m Habit: massive, fibrous, vitreous, sand crystals SG: 2.3; H: 2 L: vitreous to dull; Str: white Col: colorless to grey Clev: perfect {010}, weak {100}, {111} Optics: Biaxial + nα= 1.520; nβ= 1.522; nγ= 1.529 Name derivation: From the Greek, gyps meaning "burned" mineral. Selenite from the Greek in allusion to its pearly luster

(moon light) on cleavage fragments.

Sulfate Minerals

Gypsum (CaSO4·2H2O) Occurrence: evaporite mineral; classic sabkha deposit Associated Mins: anhydrite, halite, dolomite (evaporites) Can be confused with: ulexite (satin spar) Uses: building materials

Sulfate Minerals

Anhydrite (CaSO4) Crystal: Orthorhombic Pt. Group: 2/m 2/m 2/m Habit: massive, fibrous (rare) SG: 2.97;H: 3.5 L: vitreous to dull; Str: white Col: colorless to grey Clev: perfect [010]. [100], good [001] Optics: Biaxial + nα= 1.570; nβ= 1.576; nγ= 1.614

Name derivation: Greek anhydros, meaning "waterless"

Sulfate Minerals

Anhydrite (CaSO4) Occurrence: evaporite mineral (related to gypsum), less common in granite ore bodies and altered igneous rocks (“gangue”) Associated Mins: gypsum, halite, dolomite (evaporites); zeolites in altered igneous rocks Can be confused with: dolomite, calcite, gypsum, barite Uses: building materials

Sulfate Minerals

Celestine/Celestite (SrSO4) Crystal: Orthorhombic Pt. Group: 2/m 2/m 2/m Habit: euhedral blocky crystals common SG: 4.0; H: 3 to 3.5 L: vitreous; Str: white Col: colorless to blue Clev: perfect [001]; good [210] Optics: Biaxial + nα= 1.622; nβ= 1.624; nγ= 1.631

Name derivation: Latin coelestis, meaning “celestial"

Sulfate Minerals

Celestine/Celestite (SrSO4) Occurrence: sedimentary deposits (associated with evaporite minerals) and in epithermal vein deposits. Rarer as a cave precipitate. Associated Mins: gypsum, halite, dolomite (evaporites), sulfur, fluorite Can be confused with: barite Uses: principle source of strontium

Sulfate Minerals

Wulfenite (PbMoO4) Crystal: Tetragonal Pt. Group: 4/m Habit: euhedral tabular crystals SG: 6.75; H: 3 L: vitreous; Str: yellowish-white Col: orange to yellow Clev: poor [101] Optics: uniaxial - ne= 2.304; nw= 2.402

Name derivation: Named after the Austrian mineralogist, Frantz Xaver von Wulfen (1728-1805)

Molybdate Minerals

Wulfenite (PbMoO4) Occurrence: secondary (supergene?) product in lead and molybdenum sulfide ore deposits Associated Mins: pyromorphite, vanadinite, calcite Can be confused with: vanadinite Uses: secondary source of Mo

Molybdate Minerals

Phosphates etc.

Apatite Group (Ca5(PO4)3(F,Cl,OH) Fluorapatite (Ca5(PO4)3(F)

Crystal: Hexagonal Pt. Group: 6/m Habit: hexagonal crystals common, massive SG: 3.19; H: 5 L: vitreous; Str: white Col: you name it, you’ll see it Clev: indistinct Optics: uniaxial - ne= 1.630; nw= 1.633

Name derivation: Greek apatao, meaning “misleading"

Phosphate Minerals

Apatite (Ca5(PO4)3(F,Cl,OH) Occurrence: common. Igneous rocks, metamorphic rocks, crusts in altered biogenic remains (guano + coral) Associated Mins: varied (reflects wide occurrence) Can be confused with: beryl, corundum; diopside and olivine when massive Uses: primary mineral source of phosphorus (fertilizer)

Phosphate Minerals

Wavellite (Al3(PO4)2(OH)3·2H2O) Crystal: Orthorhombic Pt. Group: 2/m 2/m 2/m Habit: acicular, radiating crystals, globular SG: 2.34; H: 3.5-4 L: vitreous-waxy; Str: white Col: shades of green/greenish yellow Clev: prefect [110], good [101] Optics: Biaxial + nα= 1.530; nβ= 1.682; nγ= 1.686

Name derivation: Named after British mineralogist William Wavell (? To 1829)

Phosphate Minerals

Wavellite (Al3(PO4)2(OH)3·2H2O)

Occurrence: secondary mineral in aluminum-poor metamorphic rocks (e.g., Arkansas) Associated Mins: basic aluminum phosphates Can be confused with: nothing I can think of Uses: nothing

Phosphate Minerals

Pyromorphite (Pb5(PO4)3Cl) Crystal: Hexagonal Pt. Group: 6/m Habit: globular to slender prismatic crystals SG: 6.85; H: 3.5-4 L: vitreous to resinous; Str: white Col: green, yellow to brown Clev: imperfect Optics: unaxial - ne= 2.049; nw= 2.059

Name derivation: Greek for “fire” (pyr) and “form” (morfe)

Phosphate Minerals

Pyromorphite (Pb5(PO4)3Cl)

Occurrence: secondary minerals product in oxidized zones of lead Associated Mins: limonite, cerussite, malachite Can be confused with: mimetite, malachite (if you’re having a bad day) Uses: bookendite

Phosphate Minerals

Vanadinite (Pb5(VO4)3Cl ) Crystal: Hexagonal Pt. Group: 6/m Habit: hexagonal to prismatic crystals SG: 6.94; H: 3.5-4 L: vitreous; Str: brownish-yellow Col: brown to orange to yellow Clev: none Optics: uniaxial - ne= 2.35; nw= 2.416

Name derivation: Named for its vanadium content

Vanadate Minerals

Vanadinite (Pb5(VO4)3Cl )

Occurrence: secondary product in oxidized galena ore deposits Associated Mins: pyromorphite, wulfenite, calcite Can be confused with: wulfenite Uses: secondary source of Vanadium

Vanadate Minerals

Phosphate Economics “Phosphate Rock” (World Data) in 1000s of tons

Phosphate Chemistry Phosphorite is a sedimentary (biogenic) rock consisting of “collophane”, cryptocrystalline masses of apatite group minerals: Fluorapatite Ca5(PO4)3F Hydroxyapatite Ca5(PO4)3OH Chlorapatite Ca5(PO4)3Cl Bromapatite Ca5(PO4)3Br Florida is a major producer of PO4

3-

Phosphate Chemistry

Phosphorite is a common marine deposit....

http://oceanexplorer.noaa.gov/explorations/islands01/log/sep28/media/ledges.html

http://benkolstad.net/?p=2294

“Phosphate Hardground”

e.g., Florida during the Miocene

Phosphate Chemistry But thick deposits are kind of rare and require sea level change:

•Upwelling brings nutrient laden water onto the shelf •slow sedimentation restricts input of other materials (sea level rise induced hiatus?) •sea level fall removes CO3

2- and organic material

http://www.oceanoasis.org/teachersguide/activity6.html

nodular phosphate

Phosphate Chemistry Other types of phosphate/phosphorite formation: •Bone beds •Guano (“Island Deposits”)

•BIFs (Australia)

•Igneous (alkaline intrusions +/- carbonate)

http://www.fao.org/docrep/007/y5053e/y5053e07.htm

GY 302: Crystallography and Mineralogy

Lecture 15: Sulfates and Phosphates

Instructor: Dr. Doug Haywick dhaywick@southalabama.edu

This is a free open access lecture, but not for commercial purposes.

For personal use only.