GY 302: Crystallography & Mineralogy

Lecture 24: Phyllosilicates 2 Serpentine and Clays

UNIVERSITY OF SOUTH ALABAMA

Last Time

Phyllosilicates 1 General chemistry/structure Phyllosilicate classification

Mica, chlorite and talc groups

Phyllosilicate Minerals

(excludes clays, serpentine groups, and others)

Phyllosilicate Structure Phyllosilicate Structure

(Mica)

Si4O104-

cross sectional view

Phyllosilicate Classification

1:1 Structure (kaolinite, serpentine halloysite,

Chrysotile, allophane)

2:1 Structure (Most micas and clays)

1:1 & 2:1 Interlayered (Chlorite Group)

Phyllosilicate Structure

Perfect Basal Cleavage

C-axis

Today’s Agenda

Phyllosilicates 2 1. Serpentine Group

2. Other Phyllosilicates 3. Clay 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,H3O)(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

Phyllosilicates Si:O ratio = 2:5 (3 shared oxygens)

Anion component: Si4O10

-4 or Si8O20-8

With Al substitution: AlSi3O10-5 or Al2Si2O10

-6

General Formula: XYAlSi3O10(OH)2 X = K+, Na+, Li+, Ca2+

Y = Fe2+/3+, Mg2+, Al3+, rarely Cr3+, Ni3+, Mn3+

Example (“Smectite”): (Na,Ca)0-3(Al,Mg)2Si4O10(OH)2·n(H2O)

Phyllosilicate Structure Tetrahedral layers

(mostly SiO44-)

Octahedral layers (variable; Al/Mg/OH)

Cation layers (K+, Mg2+, Na+ etc.)

also H2O (clays)

Phyllosilicate Structure The octahedral layers are given specific names according to the nature of the “filling”. Need 6 x OH for octahedral coordination

Phyllosilicate Structure The octahedral layers are given specific names according to the nature of the “filling”. Need 6 x OH for octahedral coordination Al2(OH)6 = Gibbsite Layer (Al(OH)3) 2 x Al = dioctahedral coordination Mg3(OH)6 = Brucite Layer (Mg(OH)2) 3 x Mg = trioctahedral coordination

Phyllosilicate Classification Is rather nasty, but most are either monoclinic or triclinic. Classification is further done of the basis of: 1. composition of octahedral layer 2. repeat distance (distance between T-O-T “sandwiches”) 3.Whether structure is expandable (clays) 4. Number of layers in the “sandwiches” (2 versus 3)

Phyllosilicate Minerals (Serpentine Group)

Phyllosilicate Minerals (Serpentine Group)

Named because of its resemblance to snake skin

http://webmineral.com/specimens/picshow.php?id=1377

Occurrence: alteration of ultramafic minerals

“Serpentine” (antigorite)

[(Mg, Fe, Ni)3Si2O5(OH)4 ] Crystal: Monoclinic Pt. Group: m Habit: Acicular (“fibrous”) SG: 2.5 to 2.6; H: 3.5 to 4 L: silky, greasy, waxy; Str: green- white Col: white, yellow, green to black Clev: good [001] Optics: Biaxial (-); bir=0.005-0.006 nα=1.555; nβ=1.56, nγ=1.56

Chrysotile [Mg3Si2O5(OH)4]

Crystal: Monoclinic Pt. Group: 2/m Habit: Acicular (“fibrous”) SG: 2.53; H: 2.5 L: silky; Str: grey Col: green Clev: good [110], [010] Optics: Biaxial (?); bir=0.010 nα=1.569; nβ=?, nγ=1.57

Phyllosilicate Minerals (Serpentine Group)

Named from the Greek chrysos - "gold" and tilos - "fiber."

http://webmineral.com/specimens/picshow.php?id=1377

(Incl. clinochrysotile and orthochrysotile)

Occurrence: metamorphic rocks (Quebec, Canada)

“Tiger’s Eye” [Mg3Si2O5(OH)4]

Crystal: N/A Pt. Group: N/A Habit: Acicular (“fibrous”) SG: 2.65; H: 7 L: silky; Str: N/A Optics: N/A Col: yellow gold to red Clev: N/A

Phyllosilicate Minerals (Serpentine Group)

http://www.twistedtree.org.uk/Tigers_Eye_2.JPG

Prehnite [Ca2Al(AlSi3O10)(OH)2]

Crystal: Orthorhombic Pt. Group: 2mm (or mm2) Habit: globular, stalactitic SG: 2.87; H: 6 to 6.5 L: vitreous, waxy, pearly; Str: white Col: colourless (yellowish, greenish) Clev: good [001] Optics: Biaxial (+); bir=0.022-0.033 nα=1.61; nβ=1.615, nγ=1.632 Occurrence: hydrothermal

Ino-Phyllosilicate “Hybrids*”

http://webmineral.com/specimens/picshow.php?id=1377

Named after Dutch Colonel, H. Von Prehn (1733-1785).

* A mixed inosilicate-phyllosilicate mineral

Okenite [Ca3Si6O15)•6H2O]

Crystal: Triclinic Pt. Group: 1 Habit: fibrous (spherical aggregates) SG: 2.31; H: 5 L: pearly; Str: white Col: white (yellowish, bluish) Clev: good [001] Optics: Biaxial (-); bir=0.003-0.010 nα=1.512; nβ=1.514, nγ=1.515 Occurrence: secondary alteration of basalt

Ino-Phyllosilicate “Hybrids*”

Named for Lorenz Oken(1779-1851).

* A mixed inosilicate-phyllosilicate mineral

http://webmineral.com

Astrophyllite Group K2Na(Fe++,Mn)7Ti2Si8O26(OH)4

Crystal: Triclinic Pt. Group: 1 Habit: bladed (radiating) SG: 3.34; H: 3 to 3.5 L: vitreous, pearly; Str: yellowish-brown Col: brown-bronze (yellow-green) Clev: perfect [001] Optics: Biaxial (+); bir=0.050 nα=1.680; nβ=1.700, nγ=1.730 Occurrence: igenous syenites (zircon-bearing)

http://webmineral.com/specimens/picshow.php?id=1377

* A mixed inosilicate-phyllosilicate mineral

From the Greek aster - "star" and fyllon - "leaf."

Ino-Phyllosilicate “Hybrids*”

Kaolinite [Al2Si2O5(OH)4 ]

Crystal: Triclinic Pt. Group: 1 Habit: platy (microscopic) SG: 2.6; H: 1.5 to 2 L: earthy; Str: white Col: white (variable shades) Clev: perfect [001] Optics: Biaxial (-); bir=0.007 nα=1.553; nβ=1.559, nγ=1.56 Occurrence: sedimentary alteration

Phyllosilicate Minerals (“Clay” Group)

Named after Kao-Ling, China in reference to porcelain pottery

Phyllosilicate Minerals (“Clay” Group)

SEM image Kaolinite [Al2Si2O5(OH)4 ]

Crystal: Triclinic Pt. Group: 1 Habit: platy (microscopic) SG: 2.6; H: 1.5 to 2 L: earthy; Str: white Col: white (variable shades) Clev: perfect [001] Optics: Biaxial (-); bir=0.007 nα=1.553; nβ=1.559, nγ=1.56 Occurrence: sedimentary alteration

Phyllosilicate Minerals (“Clay” Group)

Named in 1937 for the state of Illinois where the mineral was first described.

SEM image Illite (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2·(H2O)

Crystal: Monoclinic Pt. Group: 2/m Habit: wispy (microscopic) SG: 2.75; H: 1 to 2 L: earthy; Str: white Col: white (variable shades) Clev: perfect [001] Optics: Biaxial (-); bir=0.030-035 nα=1.535; nβ=1.555, nγ=1.565 Occurrence: sedimentary (marine) alteration

Smectite (Montmorillonite) [(Na,Ca)0-3(Al,Mg)2Si4O10(OH)2·n(H2O) ] Crystal: Monoclinic Pt. Group: 2/m Habit: platy (microscopic) SG: 2.35; H: 1.5 to 2 L: earthy; Str: white Col: white (variable) Clev: perfect [001] Optics: Biaxial (-); bir=0.015-0.020 nα=1.485; nβ=1.504, nγ=1.505 Occurrence: sedimentary

Phyllosilicate Minerals (“Clay” Group)

Named after Veinne, Montmorillone, France

SEM image

Chlorite (Chlinochore) (Mg,Fe)3(Al,Si)4O10(OH)2(Mg,Fe)3(OH)6

Crystal: Monoclinic Pt. Group: 2/m Habit: scaly, platy (microscopic) SG: 2.65; H: 2 to 2.5 L: vitreous/pearly; Str: white Col: green to black Clev: perfect [001] Optics: Biaxial (-); bir=0.005-0.011 nα=1.571; nβ=1.571, nγ=1.576 Occurrence: low grade-metamorphism, epithermal diagenesis

From the Greek klino - "oblique" and chloros - "green”

Phyllosilicate Minerals (chlorite group)

SEM image

Diatomite SiO2 (rock, not mineral)

Crystal: N/A Pt. Group: N/A Habit: N/A SG: 0.2-0.3!; H: 1 L: earthy; Str: white Col: white, cream Clev: N/A Optics: N/A Occurrence: sedimentary

Phyllosilicate Minerals

Name Derivation: From its diatom content

Phyllosilicate Geochemistry

1:1 Structure (kaolinite, serpentine halloysite,

Chrysotile, allophane)

2:1 Structure (Most micas and clays)

1:1 & 2:1 Interlayered (Chlorite Group)

Clay Geochemistry (1:1 structure)

kaolinite (Non-expandable)

K+

Halloysite (Expandable)

H2O

Clay Geochemistry (1:1 structure)

kaolinite (Non-expandable)

K+

Halloysite (Expandable)

H2O

70nm 100 nm

Clay Geochemistry (1:1 structure)

kaolinite (Non-expandable)

K+

Halloysite (Expandable)

“glycol” 70nm

Illite/Muscovite (Non-expandable)

K+

Smectite (Expandable)

H2O

Clay Geochemistry (2:1 structure)

Illite/Muscovite (Non-expandable)

K+

Smectite (Expandable)

Clay Geochemistry (2:1 structure)

100 nm 170 nm

“glycol”

Clay Mineral Analysis

Clay Mineral Analysis

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

All images in the latter part of this lecture, unless otherwise stated, are stolen from:

http://pubs.usgs.gov/of/2001/of01-041/htmldocs/clays/kaogr.htm

Clay Mineral Analysis

Clay Mineral Analysis

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

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

Clay Mineral Analysis

Clay Mineral Analysis

Clay Mineral Analysis

Clay Mineral Analysis CHLORITE

Today’s Stuff To Do 1. Posters in for printing: One Week Today - 5:00 PM

2. Inosilicates minerals quiz 12:15-12:45 PM 3. No online lecture this week

Next Time 1. No Lecture……

2. Final exam 100 mineral list next Thursday

GY 302: Crystallography and Mineralogy

Lecture 24: Silicates 7: Clays and XRD

Instructor: Dr. Doug Haywick dhaywick@southalabama.edu

This is a free open access lecture, but not for commercial purposes.

For personal use only.