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UNIVERSITY OF SOUTH ALABAMA

GY 302: Crystallography & Mineralogy

Lecture 25: Class VIII-Silicates Tektosilicates part 1: Last Time (before the poster session)

Class VIII (Phyllosilicates) A) Serpentine Group B) Other Phyllosilicates C) Minerals (chemistry, modes of analysis)

More Phyllosilicate Minerals

Mineral Formula System

“Clay” Minerals

Kaolinite Al2Si2O5(OH)4 Triclinic *”Smectite” (Na,Ca)0-3(Al,Mg)2Si4O10(OH)2·n(H2O) Monoclinic *Bentonite (Na,Ca)0-3(Al,Mg)2Si4O10(OH)2·n(H2O) Monoclinic *Illite (K,H2O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2·(H2O) Monoclinic

Serpentine Group (17 minerals)

”Serpentine” (Mg, Fe, Ni)3Si2O5(OH)4 Monoclinic *Antigorite Mg3Si2O5(OH)4 Monoclinic Chrysotile Mg3Si2O5(OH)4 Monoclinic

Other Phyllosilicates

Stilpnomelane (series) ~K(Fe, Al)10Si12O30(OH)2 Triclinic Prehnite (series) Ca2Al(AlSi3O10)(OH)2 Orthorhombic Sepiolite Mg4Si6O15(OH)2·6(H2O) Orthorhombic Garnierite (Ni,Mg)4Si6O15(OH)2·6(H2O) Orthorhombic Apophylite KCa4(Si4O10)2F·8(H2O) Tetragonal ++ Astrophyllite** K2Na(Fe ,Mn)7Ti2Si8O26(OH)4 Triclinic Clay Geochemistry (1:1 structure) Halloysite (Expandable)

70nm 100 nm

+ K H2O

kaolinite (Non-expandable) Clay Geochemistry (2:1 structure) Smectite (Expandable)

+ K H2O

Illite/Muscovite (Non-expandable) Clay Geochemistry (2:1 structure) Smectite (Expandable)

100 nm 170 nm K+ “glycol”

Illite/Muscovite (Non-expandable) Clay Analysis

Is primarily done using XRD (X-ray diffraction). In order to understand how this works, you need to consider physics (yuck). Clay Mineral Analysis

Is primarily done using XRD (X-ray diffraction). In order to understand how this works, you need to consider physics (yuck). Clay Mineral Analysis Today’s Agenda

Class VIII Minerals (Tektosilicates) 1. Quartz Group Tektosilicate Minerals

Mineral Formula System

Quartz Group

Quartz SiO2 (multiple varieties) Trigonal * SiO2 Tetragonal SiO2 Monoclinic SiO2 “non crystalline” SiO2·nH2O “non crystalline”

*”” SiO2 (multiple varieties) “non crystalline”

Basic chemical composition: SiO2 Tektosilicate Minerals (Quartz Group) Quartz

[SiO2]

Crystal: Hexagonal (Trigonal) Pt. Group: 32 Habit: bipyramidal, massive, drusy etc. SG: 2.65; H: 7 L: vitreous; Str: colourless Col: colourless (varied)

Clev: poor [0110] http://webmineral.com Optics: Uniaxial (-); bir=0.009 Name Derivation: From the German “quarz” of nw=1.544; ne=1.553 uncertain origin Occurrence: widespread Quartz Varieties [SiO2]

Agate - banded variety of chaledony - purple Avanturine - translucent chalcedony - flesh red chalcedony Cat's Eye - chatoyant Chalcedony - microcrystalline quartz Chert - quartz - apple green chalcedony Citrine - yellow - microcrystalline quartz Hornstone - flint - red or brown chalcedony Moss - variety of chaledony Plasma - green chalcedony Prase - leek green chalcedony Rock Crystal Rose Quartz - rose colored http://webmineral.com Sapphire Quartz - blue colored - brown to black Tiger Eye - entombed asbestos Tektosilicate Minerals (Quartz Group) Coesite

[SiO2]

Crystal: Monoclinic Pt. Group: 2/m Habit: spherical masses SG: 2.93; H: 7.5 L: vitreous; Str: colourless Col: colourless (varied) Clev: none Optics: Biaxial (+); bir=0.005-0.006 http://webmineral.com nα=1.593; nβ=1.595, nγ=1.599 Named for Loring Coes, Jr. (1915-1973), American chemist, who first synthesized the phase. Occurrence: High temp/pressure (impact sites) Tektosilicate Minerals (Quartz Group) Cristabolite

[SiO2]

Crystal: Tetragonal Pt. Group: 422 Habit: spherical masses SG: 2.27; H: 6.5 L: vitreous; Str: white Col: blue-grey, brown, yellow

Clev: none http://webmineral.com Optics: Uniaxial (-); bir=0.002-0.004 n =1.486; n =1.482 w e Name Derivation: From its location, Cerro San Occurrence: void-fill in felsic rocks with Cristobal, Mexico. topaz and garnet

Tektosilicate Minerals (Quartz Group) Chalcedony

[SiO2·?H2O]

Crystal: N/A Pt. Group: N/A Habit: massive (fibrous in TS) SG: 2.57-2.63; H: 6.5 L: vitreous to waxy; Str: white Col: blue-grey (colourless)

Clev: none http://webmineral.com cryptocrystalline Optics: Chalcedony in the main ingredient in “chert” Occurrence: diagenetic void-fill but much chalcedony itself may be composed of another quartz ; “morganite” Tektosilicate Minerals (Quartz Group) Opal

[SiO2·nH2O]

Crystal: N/A Pt. Group: N/A Habit: massive (veinlets) SG: 2.09; H: 5.5 to 6 L: vitreous, dull, waxy; Str: white Col: varied

Clev: none http://webmineral.com Optics: isotropic; n=1.43-1.46 Occurrence: hot springs, petrified

wood, biogenic Name Derivation: From the Old Indian upala - "precious stone." Tektosilicate Minerals (Quartz Group) “Chert”

[SiO2]

Crystal: N/A Pt. Group: N/A Habit: microcrystalline SG: 2.09-2.65; H: 5.5 to 7 L: dull, waxy; Str: white Col: varied

Clev: none http://www.uky.edu/KGS/rocksmn/images/chert_var.jpg Optics: N/A Chert is a rock name. Numerous varieties of chert have been identified. Occurrence: sedimentary Tektosilicate Minerals (Quartz Group) Lechatlerite (“)

[SiO2+ contaminants]

Crystal: N/A Pt. Group: N/A Habit: Amorphous? SG: 2.20; H: 7.0? L: dull; Str: white Optics: N/A Col: white Clev: none http://www.mindat.org/gphotos/0707699001129998806.jpg Occurrence: strikes Lightning strikes may pass 1,000,000 volts of electricity into the ground fusing quartz into “”. Six Quartz Polymorphs

Displacive polymorphic transformations require relatively minor changes in the crystal lattice (e.g., modification of α, β or γ crystallographic angles). There is generally no change in energy at the transformation threshold so polymorphic transformations are instantaneous and reversible. Six Quartz Polymorphs

Displacive polymorphic transformations require relatively minor changes in the crystal lattice (e.g., modification of α, β or γ β-quartz If you heat “quartz” crystallographic angles). above 600 ºC it There is generally no change transforms to the α- in energy at the polymorph (also known transformation threshold so as high quartz). When the polymorphic temperature falls below transformations are 600ºC it transforms back instantaneous and reversible. to the β- polymorph (also α-quartz known as low quartz). Six Quartz Polymorphs

Displacive polymorphic transformations require relatively minor changes in the crystal lattice (e.g., modification of α, β or γ The higher the pressure crystallographic angles). of formation, the higher There is generally no change the specific gravity. in energy at the transformation threshold so polymorphic transformations are instantaneous and reversible.

Specific Gravity

67 km 220 km Quartz Phase Diagrams

Olivine-Enstatite-Quartz System Quartz Phase Diagrams

Quartz-Nephaline-Kalsilite System

We could look at several other

SiO2 phase diagrams, but that would leave Dr. Allison with nothing to torment you with in GY 303. Quartz: Last Words

The quartz minerals are one of the most pervasive groups on our planet. (Occurrence = everywhere)

•Igneous (Bowen’s Reaction Series) •Sedimentary (Diagenesis) •Metamorphic (low to high grade) •Hydrothermal (epithermal ore emplacement)

Quartz: Last Words

Except for 2 situations:

1) Nephaline*-bearing rocks

NaAlSiO4 + 2SiO2 → NaAlSi3O8 (albite)

2) Corundum-bearing rocks

Al2O3 + SiO2 → Al2SiO5 (Sil/And/Ky)

* A feldspathoid; you’ll hear about these next time Today’s Stuff To Do 1. Poster Session next Tuesday (posters due to Doug by 5 PM today) They will be printed by 2 PM Thursday 2. Phyllosilicates quiz in 1 hr 3) Final lab test/mineral notebook exam (2 weeks) 100 mineral lab final list (Thursday)

Next Time

1. Poster Prep period (no class meeting) GY 302: Crystallography and Mineralogy

Lecture 25: Silicates 8: Quartz Group

Instructor: Dr. Doug Haywick [email protected]

This is a free open access lecture, but not for commercial purposes. For personal use only.