Chapter 23

1. Chapter 23 Sulfates, phosphates and related minerals Apatite as a biogenic mineral

2. Introduction • Fundamental building block: • PO43- (phosphates) or SO42- (sulfates) tetrahedron • Several phosphate structures identical to silicate structures • Berlinite (AlPO4) – quartz (SiO2) • Triphyline (LiFePO4) – olivine (Mg2SiO4) • Xenotime (YPO4) – zircon (ZrSiO4) • Mostly isolated polyhedraunlike most silicates were tetrahedrons are polimerized into sheets, chains, frameworks • Phosphates are related to arsenates (AsO43-), vanadates (VO43-) and tungstates (WO42-) • Economic interest: apatite, gypsum, scheelite

3. Classification Class VIII: Phosphates, arsenates and vanadates Class IX: Sulfates Class X: Tungstates and Molybdates Class XI: Chromates Class XII: Nitrates

4. Class VIII: Phosphate, arsenates and vanadates (Table 23.1) • 250 minerals; very small amount of earth’s crust • Apatite very important • Be-Al-Mg association • Variscite-Strengite Group • Lazulite Group • Fe-Mn-Na association • Pharmacosiderite Group • Triphyline Group • Na-Ca-REE association • Apatite Group • Monazite Group • Zn-Cu-Pb association • Tarbuttite-Adamite Group • Pyromorphite Group • Descloizite Group • Tobernite-Zeunerite Group • Carnotite Group

5. Na-Ca-REE associationApatiteCa5(PO4)3(F,Cl,OH) Single phosphate Hexagonal Fluorapatite (F), chlorapatite (Cl), hydroxylapatite (OH), carbonylapatite (CO3) Can contain Sr or Ce Well-developed crystals: prismatic, ending with pinacoidal faces Occurrence: widespread; usually as small grains – largest grains in granite, pegmatites and marbles; can make up 80 wt% of alkaline rocks Used as fertilizer

6. Na-Ca-REE associationMonaziteCePO4 Contains other REE, as well as Th and U Found in granite pegmatites: resembles garnet, but have cleavage and lower hardness As minute inclusions in gneisses: usually in cordierite producing pleochroic halos Mined from river and coastal sands as REE, Th and U source

7. Zn-Cu-Pb-(U) AssociationUranium micas • Torbernite (Cu2(UO2)2(PO4)2.10H2O • Autunite (Ca(UO2)2(PO4)2.10H2O • Carnotite (K2(UO2)2(VO4)2.3H2O • Occur as powdery aggregates or platy crystals • High radioactivity • Carnotite: ore for vanadium and uranium

8. TurquoiseCuAl6(PO4)4(OH)8.4H2O • Cryptocrystalline • Blue – blue-green aggregates • Secondary mineral in veins of altered volcanic rocks • Rare gemstone

9. Class IX: Sulfates(Table 23.2) • Salt of sulfuric acid: H2SO4 • Important associations: • Na(K)-Ca-Ba association • Anhydrite • Gypsum • Celestite • Barite • Cu-Pb-Zn association • Chalcanthite • Anglesite

10. AnhydriteCaSO4 • Evaporite mineral • Hydrothermal sulfide ore deposits • Some metamorphic rocks • Does not react with HCl • Raw material for cement production

11. GypsumCaSO4.2H2O • Evaporite mineral • Forms alternating layers with anhydrite and halite precipitating from solutions • Hydrothermal mineral from meteoric water • On surface of clay or sand – flower-like morphology (desert rose) • Mostly flattened and prismatic crystals; distinctive swallowtail twins very common • Use: cement and plaster in construction industry

12. Celestite and Barite(SrSO4 and BaSO4) • Limited solid solution • Found in druses and granular aggregates • Forms in • Barite: Hydrothermal deposits • Celestite: Secretions in sedimentary rocks • Uses • Barite: paint, in chemical, rubber, paper industries, drilling additive • Celestite: sugar manufacturing, pyrotechnology, pharmaceuticals

13. AnglesitePbSO4 • Massive granular and colloform aggregates • Prismatic-tabular crystals • Product of galena oxidation • High S.G. • So does barite and cerussite • Anglesite and cerussite often associated with galena, barite not • Cerussite, PbCO3, effervesce with HCl

14. AluniteKAl3(SO4)2(OH)6 • Hydrothermal alteration of felsic rocks • Felsic volcanic rocks interact with sulfuric hydrothermal solutions • 3KAlSi3O8 + 2SO42- + 10H+ K-feldspar KAl3(SO4)2(OH)6 + 9SiO2 + 2K+ + 4H2O Alunite • Aluminum ore and source of K

15. Class X: Tungstates • Closely related to sulfates • WO42-tetrahedra instead of SO42- • Wolframite • Isomorphic series: FeWO4-MnWO4 • Monoclinic • Mistaken for sphalerite: • Sphalerite has several cleavages, isometric crystals, lower density • Forms in quartz veins and placers • Tungsten ore • Scheelite • CaWO4 • Forms in quartz veins and in skarns • Can be mistaken for quartz or calcite • Blue and white fluorescence diagnostic; much softer than quartz; heavier than calcite • Major tungsten ore

16. Biogenic processes • Biogenic minerals forms in surface environments by: • Transformations of primary organic aggregates or • Biochemical processes • Originate from living organisms or with their assistance • Not strictly minerals, but is the same substance as produced inorganically in rocks • Crystallize within organism and are surrounded with organic material • Bones & teeth: platy crystals closely related to carbonate-hydroxylapatitesuspended in protein – comprise up to 70% of dried bones • Various minerals in: mollusk shells, corals, trilobites, algae, egg shells • Aragonite in mother-of-pearl • Kidney stones, gall stones • 80 different minerals in fossil and recent animals and plants • Calcite in eye-lenses in extinct trilobites and on body of eyeless brittlestar (starfish) • Magnetite: biomineralogical navigation system for pigeons, bacteria • Bacteria NB in formation of some ore deposits and weathering processes • Table 23.3