Mineral Quiz 3 results

UNIVERSITY OF SOUTH ALABAMA

GY 302: Crystallography & Mineralogy Lectures 18: Class VIII-Silicates (Olivine Group) Instructor: Dr. Douglas Haywick

Last Time (on line) 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.

Phosphates etc.

Sulfate Minerals 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 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"

Molybdate 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)

Phosphate Minerals 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 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)

Vanadate 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

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 PO43-

Today’s Agenda Class VIII Minerals Basic classification of silicates Nesosilicates (Olivine, Garnet Groups, Aluminum Silicates) 3. Olivine Group 1.

2.

Mineral Classes Class I

Name Native Elements

Anion(s)

none

Examples

Dominant Bond

Metals: Gold, Copper, Silver Semi-metals: Arsenic (As) Non-metals: diamond, graphite, sulfur

Metallic

Covalent

II

Sulfides

S-

Pyrite, Chalcopyrite, Galena

III

Oxides\hydroxides

O2- OH-

hematite, magnetite, limonite

IV

Halides

Cl-, Fl-

halite, fluorite

V

Carbonates

CO32-

calcite, aragonite, malachite

VI

Sulfates

SO42-

gypsum, anhydrite

VII

Phosphates

PO43-

apatite

VIII

Silicates

SiO44-

>3000 (i.e., most minerals)

Largely Ionic

Mineral Classes Class I

Name Native Elements

Anion(s)

none

Examples

Dominant Bond

Metals: Gold, Copper, Silver Semi-metals: Arsenic (As) Non-metals: diamond, graphite, sulfur

Metallic

Covalent

II

Sulfides

S-

Pyrite, Chalcopyrite, Galena

III

Oxides\hydroxides

O2- OH-

hematite, magnetite, limonite

IV

Halides

Cl-, Fl-

halite, fluorite

V

Carbonates

CO32-

calcite, aragonite, malachite

VI

Sulfates

SO42-

gypsum, anhydrite

VII

Phosphates

PO43-

apatite

VIII

Silicates

SiO44-

>3000 (i.e., most minerals)

Largely Ionic

Silicate Classification

SiO4

4The basic silicate tetrahedra

Silicate Classification Covalent radius of Si = 1.11 A Ionic radius of Si4+ = 0.41 A Covalent radius of O = 0.73 A Ionic radius of O2- = 1.40 A

The basic silicate tetrahedra

Silicate Classification Covalent radius of Si = 1.11 A Ionic radius of Si4+ = 0.41 A Covalent radius of O = 0.73 A Ionic radius of O2- = 1.40 A

So what? SiO4 tetrahedra is 40% ionic and 60% covalent in character and the bond can be “polymerized”

The basic silicate tetrahedra Chalk board

Silicate coordination A-X ratios (e.g., Si-O or Al-O) =

rA rX

rAl3+ = 0.37 rO2-

Magic number for A-X to switch from tetragonal to octahedral coordination is 0.414

A-X = 0.732 to 0.414 (octahedral, 6 fold) A-X = 0.225 to 0.414 (tetrahedral, 4 fold)

octahedral

tetragonal


SiO4



SiO4



Nesosilicate Structure (plan model) Cations

Nesosilicate Structure (3D model) down up Mg2+ down (z = -1/2)

Mg2+ up (z = 0)

Nesosilicates

Nesosilicate Minerals Olivine Group Fayalite (Fe2SiO4); Forsterite (Mg2SiO4) Crystal: Orthorhombic Pt. Group: 2/m 2/m 2/m Habit: prismatic, granular Forsterite (named after Johann Forster, German naturalist ) SG: 3.2; H: 6.5 L: vitreous; Str: white Col: colorless-green (For) yellow (Fay) Clev: good (010), poor (100) Optics: Biaxial +/nα= 1.651; nβ= 1.670; nγ= 1.689 Fayalite (named after the Fayal Island, Azores)

Nesosilicate Minerals Olivine Group Fayalite (Fe2SiO4); Forsterite (Mg2SiO4) Occurrence: ultramafic and basaltic igneous rocks (peridotite, dunite, komatiite) Associated Mins: pyroxenes, chromite Can be confused with: when fine grained, quartz, pyroxene Uses: peridot (gemstones) http://som.web.cmu.edu/structures/S086-forsterite.html

Nesosilicates

Olivine Minerals Mineral Chemical Composition Forsterite Mg2SiO4 Fayalite Fe2SiO4 Monticellite CaMgSiO4 Kirschsteinite CaFeSiO4 Tephroite Mn2SiO4

http://gore.ocean.washington.edu/classpages/ocean410_2001/notes/unit09_fi les/image007.gif

Nesosilicates Bowen’s Reaction Series

Nesosilicates Xenoliths: •Inclusions of rocks within other igneous rocks

Ophiolite Complexes Orogenic Belts •Rare slices of the deep lithosphere and upper mantle •Gros Morne National Park (Table Mountain)

http://members.shaw.ca/ph-design/BettsCove/

http://volcano.oregonstate.edu/ophiolites

Ophiolite Complexes Orogenic Belts •Rare slices of the deep lithosphere and upper mantle •Gros Morne National Park (Table Mountain)

Nesosilicates Phase Diagrams

http://www.geoclassroom.com/mineralogy/olivine_melting.gif

Nesosilicates


Nesosilicates


Nesosilicates


Nesosilicates


Nesosilicates


Today’s Stuff To Do Ore Assessment exercise due next week

1.

Today’s Lab Soup! Quiz 6 (Halides and Carbonates 1:00 -1:20 PM) 1.

2.

On Line Lecture Lecture 19 (Silicates 2: Garnet Group)

1.

Thursday 1.

Writing Assignment discussion

GY 302: Crystallography and Mineralogy Lecture 18: Silicates 1: Olivine Group Instructor: Dr. Doug Haywick [email protected] This is a free open access lecture, but not for commercial purposes. For personal use only.