Post on 13-Jan-2016
Chapter 23Sulfates, phosphates and
related mineralsApatite as a biogenic mineral
Introduction
Fundamental building block: PO4
3- (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 polyhedra unlike most silicates were
tetrahedrons are polimerized into sheets, chains, frameworks
Phosphates are related to arsenates (AsO43-),
vanadates (VO43-) and tungstates (WO4
2-) Economic interest: apatite, gypsum, scheelite
Classification
Class VIII: Phosphates, arsenates and vanadates
Class IX: Sulfates Class X: Tungstates and Molybdates Class XI: Chromates Class XII: Nitrates
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
Na-Ca-REE associationApatite
Ca5(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
Na-Ca-REE associationMonazite
CePO4
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
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
TurquoiseCuAl6(PO4)4(OH)8.4H2O
Cryptocrystalline Blue – blue-green aggregates Secondary mineral in veins of
altered volcanic rocks Rare gemstone
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
AnhydriteCaSO4
Evaporite mineral Hydrothermal sulfide ore deposits Some metamorphic rocks Does not react with HCl Raw material for cement production
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
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
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
AluniteKAl3(SO4)2(OH)6
Hydrothermal alteration of felsic rocks Felsic volcanic rocks interact with
sulfuric hydrothermal solutions 3KAlSi3O8 + 2SO4
2- + 10H+
K-feldspar
KAl3(SO4)2(OH)6 + 9SiO2 + 2K+ + 4H2O
Alunite
Aluminum ore and source of K
Class X: Tungstates Closely related to sulfates
WO42- tetrahedra instead of SO4
2-
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
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-
hydroxylapatite suspended 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