GY 302: Crystallography & Mineralogy

Transcription

1 UNIVERSITY OF SOUTH ALABAMA GY 302: Crystallography & Mineralogy Lecture 15: Sulfates and Phosphates (Class VI and VII Minerals) Instructor: Dr. Douglas Haywick

2 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)

3 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 BO 4 4- which is tetrahedral Oxygen atoms are strongly covalently bonded in the anion (especially in CO 3 2- ), but bonding between the anion and the cation is ionic

4 Carbonates Calcite Group (3 2/m): Calcite (CaCO 3 ) Magnesite (MgCO 3 ) Siderite (FeCO 3 ) Rhodochrosite (MnCO 3 ) Smithsonite (ZnCO 3 ) Dolomite Group (3): Dolomite (CaMg(CO 3 ) 2 ) Ankerite (CaFe(CO 3 ) 2 ) Kutnahurite (CaMn(CO 3 ) 2 ) Zincian Dolomite (CaZn(CO 3 ) 2 )

5 Carbonates Calcite Group (3 2/m): Calcite (CaCO 3 ) Magnesite (MgCO 3 ) Siderite (FeCO 3 ) Rhodochrosite (MnCO 3 ) Smithsonite (ZnCO 3 ) Aragonite Group (2/m 2/m 2/m): Aragonite (CaCO 3 ) Witherite (BaCO 3 ) Strontianite (SrCO 3 ) Cerussite (PbCO 3 )

6 Carbonate Minerals Aragonite (CaCO 3 ) Crystal: Orthorhombic (pseudo hexagonal) Pt. Group: 2/m 2/m 2/m Habit: euhedral, hexagonal prisms SG: 2.94; H: L: vitreous; Str: white Col: colourless (pinkish) Clev: poor{010}, {110} Optics: Biaxial - n α = 1.530; n β = 1.682; n γ = Name derivation: From its type location, Aragon in Spain

7 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.

8 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

9 Sulfates etc.

10 Sulfate Minerals Gypsum (CaSO 4 2H 2 O) 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 + n α = 1.520; n β = 1.522; n γ = Name derivation: From the Greek, gyps meaning "burned" mineral. Selenite from the Greek in allusion to its pearly luster (moon light) on cleavage fragments.

11 Sulfate Minerals Gypsum (CaSO 4 2H 2 O) Occurrence: evaporite mineral; classic sabkha deposit Associated Mins: anhydrite, halite, dolomite (evaporites) Can be confused with: ulexite (satin spar) Uses: building materials

12 Sulfate Minerals Anhydrite (CaSO 4 ) 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 + n α = 1.570; n β = 1.576; n γ = Name derivation: Greek anhydros, meaning "waterless"

13 Sulfate Minerals Anhydrite (CaSO 4 ) 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

14 Sulfate Minerals Celestine/Celestite (SrSO 4 ) 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 + n α = 1.622; n β = 1.624; n γ = Name derivation: Latin coelestis, meaning celestial"

15 Sulfate Minerals Celestine/Celestite (SrSO 4 ) 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

16 Molybdate Minerals Wulfenite (PbMoO 4 ) 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 - n e = 2.304; n w = Name derivation: Named after the Austrian mineralogist, Frantz Xaver von Wulfen ( )

17 Molybdate Minerals Wulfenite (PbMoO 4 ) 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

18 Phosphates etc.

19 Phosphate Minerals Apatite Group (Ca 5 (PO 4 ) 3 (F,Cl,OH) Fluorapatite (Ca 5 (PO 4 ) 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 - n e = 1.630; n w = Name derivation: Greek apatao, meaning misleading"

20 Phosphate Minerals Apatite (Ca 5 (PO 4 ) 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)

21 Phosphate Minerals Wavellite (Al 3 (PO 4 ) 2 (OH) 3 2H 2 O) Crystal: Orthorhombic Pt. Group: 2/m 2/m 2/m Habit: acicular, radiating crystals, globular SG: 2.34; H: L: vitreous-waxy; Str: white Col: shades of green/greenish yellow Clev: prefect [110], good [101] Optics: Biaxial + n α = 1.530; n β = 1.682; n γ = Name derivation: Named after British mineralogist William Wavell (? To 1829)

22 Phosphate Minerals Wavellite (Al 3 (PO 4 ) 2 (OH) 3 2H 2 O) Occurrence: secondary mineral in aluminumpoor metamorphic rocks (e.g., Arkansas) Associated Mins: basic aluminum phosphates Can be confused with: nothing I can think of Uses: nothing

23 Phosphate Minerals Pyromorphite (Pb 5 (PO 4 ) 3 Cl) Crystal: Hexagonal Pt. Group: 6/m Habit: globular to slender prismatic crystals SG: 6.85; H: L: vitreous to resinous; Str: white Col: green, yellow to brown Clev: imperfect Optics: unaxial - n e = 2.049; n w = Name derivation: Greek for fire (pyr) and form (morfe)

24 Phosphate Minerals Pyromorphite (Pb 5 (PO 4 ) 3 Cl) 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

25 Vanadate Minerals Vanadinite (Pb 5 (VO 4 ) 3 Cl ) Crystal: Hexagonal Pt. Group: 6/m Habit: hexagonal to prismatic crystals SG: 6.94; H: L: vitreous; Str: brownish-yellow Col: brown to orange to yellow Clev: none Optics: uniaxial - n e = 2.35; n w = Name derivation: Named for its vanadium content

26 Vanadate Minerals Vanadinite (Pb 5 (VO 4 ) 3 Cl ) Occurrence: secondary product in oxidized galena ore deposits Associated Mins: pyromorphite, wulfenite, calcite Can be confused with: wulfenite Uses: secondary source of Vanadium

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

28 Phosphate Chemistry Phosphorite is a sedimentary (biogenic) rock consisting of collophane, cryptocrystalline masses of apatite group minerals: Fluorapatite Ca 5 (PO 4 ) 3 F Hydroxyapatite Ca 5 (PO 4 ) 3 OH Chlorapatite Ca 5 (PO 4 ) 3 Cl Bromapatite Ca 5 (PO 4 ) 3 Br Florida is a major producer of PO 4 3-

29 Phosphate Chemistry Phosphorite is a common marine deposit... e.g., Florida during the Miocene Phosphate Hardground

30 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 CO 3 2- and organic material nodular phosphate

31 Phosphate Chemistry Other types of phosphate/phosphorite formation: Bone beds Guano ( Island Deposits ) BIFs (Australia) Igneous (alkaline intrusions +/- carbonate)

32 GY 302: Crystallography and Mineralogy Lecture 15: Sulfates and Phosphates Instructor: Dr. Doug Haywick This is a free open access lecture, but not for commercial purposes. For personal use only.