Chapter 23

Chapter 23Sulfates, phosphates and

related mineralsApatite as a biogenic mineral

Introduction Fundamental building block:

PO43- (phosphates) or SO4

2- (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