GY 302: Crystallography & Mineralogy

Transcription

1 UNIVERSITY OF SOUTH ALABAMA GY 302: Crystallography & Mineralogy Lecture 25: Class VIII-Silicates Tektosilicates part 1: Quartz

2 Last Time (before the poster session) Class VIII Minerals (Phyllosilicates) A) Serpentine Group B) Other Phyllosilicates C) Clay Minerals (chemistry, modes of analysis)

3 More Phyllosilicate Minerals Mineral Formula System Clay Minerals Kaolinite Al 2 Si 2 O 5 (OH) 4 Triclinic * Smectite (Na,Ca) 0-3 (Al,Mg) 2 Si 4 O 10 (OH) 2 n(h 2 O) Monoclinic *Bentonite (Na,Ca) 0-3 (Al,Mg) 2 Si 4 O 10 (OH) 2 n(h 2 O) Monoclinic *Illite (K,H 2 O)(Al,Mg,Fe) 2 (Si,Al) 4 O 10 [(OH) 2 (H 2 O) Monoclinic Serpentine Group (17 minerals) Serpentine (Mg, Fe, Ni) 3 Si 2 O 5 (OH) 4 Monoclinic *Antigorite Mg 3 Si 2 O 5 (OH) 4 Monoclinic Chrysotile Mg 3 Si 2 O 5 (OH) 4 Monoclinic Other Phyllosilicates Stilpnomelane (series) ~K(Fe, Al) 10 Si 12 O 30 (OH) 2 Triclinic Prehnite (series) Ca 2 Al(AlSi 3 O 10 )(OH) 2 Orthorhombic Sepiolite Mg 4 Si 6 O 15 (OH) 2 6(H 2 O) Orthorhombic Garnierite (Ni,Mg) 4 Si 6 O 15 (OH) 2 6(H 2 O) Orthorhombic Apophylite KCa 4 (Si 4 O 10 ) 2 F 8(H 2 O) Tetragonal Astrophyllite** K 2 Na(Fe ++,Mn) 7 Ti 2 Si 8 O 26 (OH) 4 Triclinic

4 Clay Geochemistry (1:1 structure) Halloysite (Expandable) 70nm 100 nm K + H 2 O kaolinite (Non-expandable)

5 Clay Geochemistry (2:1 structure) Smectite (Expandable) K + H 2 O Illite/Muscovite (Non-expandable)

6 Clay Geochemistry (2:1 structure) Smectite (Expandable) 100 nm 170 nm K + glycol Illite/Muscovite (Non-expandable)

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

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

9 Clay Mineral Analysis

10 Today s Agenda Class VIII Minerals (Tektosilicates) 1. Quartz Group

11 Tektosilicate Minerals Mineral Formula System Quartz Group Quartz SiO 2 (multiple varieties) Trigonal *Cristobalite SiO 2 Tetragonal Coesite SiO 2 Monoclinic Chalcedony SiO 2 non crystalline Opal SiO 2 nh 2 O non crystalline * Chert SiO 2 (multiple varieties) non crystalline Basic chemical composition: SiO 2

12 Tektosilicate Minerals (Quartz Group) Quartz [SiO 2 ] 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] Optics: Uniaxial (-); bir=0.009 n w =1.544; n e =1.553 Occurrence: widespread Name Derivation: From the German quarz of uncertain origin

13 Quartz Varieties [SiO 2 ] Agate - banded variety of chaledony Amethyst - purple Avanturine - translucent chalcedony Carnelian - flesh red chalcedony Cat's Eye - chatoyant Chalcedony - microcrystalline quartz Chert - cryptocrystalline quartz Chrysoprase - apple green chalcedony Citrine - yellow Flint - microcrystalline quartz Hornstone - flint Jasper - red or brown chalcedony Moss Agate - variety of chaledony Plasma - green chalcedony Prase - leek green chalcedony Rock Crystal Rose Quartz - rose colored Sapphire Quartz - blue colored Smoky Quartz - brown to black Tiger Eye - entombed asbestos

14 Tektosilicate Minerals (Quartz Group) Coesite [SiO 2 ] 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= n α =1.593; n β =1.595, n γ =1.599 Occurrence: High temp/pressure (impact sites) Named for Loring Coes, Jr. ( ), American chemist, who first synthesized the phase.

15 Tektosilicate Minerals (Quartz Group) Cristabolite [SiO 2 ] 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 Optics: Uniaxial (-); bir= n w =1.486; n e =1.482 Occurrence: void-fill in felsic rocks with topaz and garnet Name Derivation: From its location, Cerro San Cristobal, Mexico.

16 Tektosilicate Minerals (Quartz Group) Chalcedony [SiO 2?H 2 O] Crystal: N/A Pt. Group: N/A Habit: massive (fibrous in TS) SG: ; H: 6.5 L: vitreous to waxy; Str: white Col: blue-grey (colourless) Clev: none Optics: cryptocrystalline Occurrence: diagenetic void-fill Chalcedony in the main ingredient in chert but much chalcedony itself may be composed of another quartz pseudomorph; morganite

17 Tektosilicate Minerals (Quartz Group) Opal [SiO 2 nh 2 O] 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 Optics: isotropic; n= Occurrence: hot springs, petrified wood, biogenic Name Derivation: From the Old Indian upala - "precious stone."

18 Tektosilicate Minerals (Quartz Group) Chert [SiO 2 ] Crystal: N/A Pt. Group: N/A Habit: microcrystalline SG: ; H: 5.5 to 7 L: dull, waxy; Str: white Col: varied Clev: none Optics: N/A Occurrence: sedimentary Chert is a rock name. Numerous varieties of chert have been identified.

19 Tektosilicate Minerals (Quartz Group) Lechatlerite ( Fulgurite) [SiO 2 + 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 Occurrence: lightning strikes Lightning strikes may pass 1,000,000 volts of electricity into the ground fusing quartz sand into glass.

20 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.

21 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. β-quartz α-quartz If you heat quartz above 600 ºC it transforms to the α- polymorph (also known as high quartz). When the temperature falls below 600ºC it transforms back to the β- polymorph (also known as low quartz).

22 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. The higher the pressure of formation, the higher the specific gravity. Specific Gravity 67 km 220 km

23 Quartz Phase Diagrams Olivine-Enstatite-Quartz System

24 Quartz Phase Diagrams Quartz-Nephaline-Kalsilite System We could look at several other SiO 2 phase diagrams, but that would leave Dr. Allison with nothing to torment you with in GY 303.

25 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)

26 Quartz: Last Words Except for 2 situations: 1) Nephaline*-bearing rocks NaAlSiO 4 + 2SiO 2 NaAlSi 3 O 8 (albite) 2) Corundum-bearing rocks Al 2 O 3 + SiO 2 Al 2 SiO 5 (Sil/And/Ky) * A feldspathoid; you ll hear about these next time

27 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)

28 GY 302: Crystallography and Mineralogy Lecture 25: Silicates 8: Quartz Group Instructor: Dr. Doug Haywick This is a free open access lecture, but not for commercial purposes. For personal use only.