Mineral Quizzes Results - University of South Alabama

GY 302: Crystallography & Mineralogy

UNIVERSITY OF SOUTH ALABAMA

Lecture 23: Phyllosilicates 1

Mica Minerals etc.

Last Time

Class VIII Minerals: Inosilicates (part 2)

1. Amphiboles

Inosilicates (double chain)

Two major sub groups of amphiboles are distinguished on the basis of crystal structure:

1) Orthorhombic Amphiboles 2) Monoclinic Amphiboles

http://www.uwgb.edu/dutchs/GRAPHIC0/ROCKMIN/ATOM-STRUCT/amphibchain.gif


General formula: XY((Al,Si)4O11)2(OH)2

X[larger ions] = Ca2+, Na+ Y[smaller ions] = Mg2+, Al3+, Fe2+/3+, Mn2+/3+)

http://www.tulane.edu/~sanelson/images/amphibole_cleavage.gif


http://www.tulane.edu/~sanelson/images/amphibole-compositions.gif

We recognize several amphibole series (solid solution) 1) Anthophyllite Series (Orthorhombic) 2) Cummingtonite Series (Monoclinic) 3) Actinolite Series (Monoclinic) 4) Hornblende Series (Monoclinic) 5) Glaucophane Series (Monoclinic) 6) Riebeckite Series (Monoclinic) 7) Arfvedsonite-Eckermannite Series (Mono) “Hornblende”: (Ca,Na,K)2-3(Mg,Fe,Al)5Si6(Si,Al)2O22(OH)2

“Glaucophane”: Na2Mg3Al2Si8O22(OH)2 “Riebeckite”: Na2Fe2+

3Fe3+2Si8O22(OH)2

“Arvedsonite”: Na3(Mg,Fe2+)4AlSi8O22(OH)2

Several minerals with a fibrous habit that have useful economic properties (flexible, high melting points, tensile strength, heat resistance)

Asbestos Minerals

Amphibole Asbestos minerals: Anthophyllite, Tremolite, Amosite, Actinolite, Crocidolite Serpentine Asbestos minerals: Clinochrysotile, Orthochrysotile

Crocidolite (“blue asbestos”) is part of the Riebeckite series and is the worst of the asbestos minerals (at least according to legal websites)

http://www.earthsci.unimelb.edu.au/Thomas/lteng/engeimg/enge0247a.JPG

Today’s Agenda

Phyllosilicates Part 1 1. General chemistry/structure 2. Phyllosilicate classification

3. Mica, chlorite and talc groups

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


Anion component: Si4O10

-4 or Si8O20-8

With Al substitution: AlSi3O10

-5 or Al2Si2O10-6


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 (Muscovite): KAl2 AlSi3O10(OH)2

Phyllosilicate Structure Inosilicate Structure

(Amphibole)

Si4O116-

Phyllosilicate Structure Inosilicate Structure

(Amphibole)

Si4O116-

Phyllosilicate Structure (Mica)

Si4O104-

Phyllosilicate Structure Phyllosilicate Structure

(Mica)

Si4O104-

cross sectional view

Phyllosilicate Structure

Tetrahedral layer

Tetrahedral layer

Octahedral layer

Phyllosilicate Structure Tetrahedral layers

(mostly SiO44-)

Octahedral layers (variable; Al/Mg/OH)

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

also H2O (clays)

Phyllosilicate Structure

Perfect Basal Cleavage

C-axis

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:

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

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”)

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)

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 Classification 2:1 Structure

(Most micas and clays)

Phyllosilicate Classification

1:1 Structure (kaolinite, serpentine, halloysite,

Chrysotile, allophane)

2:1 Structure (Most micas and clays)

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 Minerals

(excludes clays, serpentine groups, and others)

Biotite [K(Fe,Mg)3AlSi3O10(OH)2 ]

Crystal: Monoclinic Pt. Group: 2/m Habit: platy (flexible) SG: 2.8-3.4; H: 2.5-3 L: vitreous to pearly; Str: grey Col: brown (reddish to greenish) Clev: perfect [001] Optics: Biaxial (-); bir=0.030-0.070 nα=1.522; nβ=1.548, nγ=1.549 Occurrence: Intermediate Ig; med. grade metamorphic rocks Named after French physicist, Jean Baptiste Biot (1774 -

1862), who studied the optical properties of the micas.

Phyllosilicate Minerals (micas, 2:1 layers)


From Muscovy glass, alluding to the Russian province of Muscovy. Occurrence: pegmatitic Ig., med

grade Meta, sericite in Sed. rocks

Muscovite [KAl2 AlSi3O10(OH)2]

Crystal: Monoclinic Pt. Group: 2/m Habit: platy (flexible) SG: 2.82; H: 2 to 2.5 L: vitreous to pearly; Str: white Col: white (gold, silver, green) Clev: Perfect [001] Optics: Biaxial (-); bir=0.036-0.049 nα=1.552; nβ=1.582, nγ=1.587

Fuchsite (v. muscovite)

[K(Al,Cr)2 AlSi3O10(OH)2] Crystal: Monoclinic Pt. Group: 2/m Habit: platy (flexible) SG: 2.82; H: 2 to 2.5 L: vitreous to pearly; Str: white Col: emerald green Clev: Perfect [001] Optics: Biaxial (-); bir=0.032 nα=1.569; nβ=1.598, nγ=1.601

The Cr-variety of muscovite. The Ba-rich variety is called Binnite

http://www.dakotamatrix.com/images/products/fuchsite15805a.jpg


Occurrence: metamorphic rocks

Phlogopite (biotiote series)

[KMg3AlSi3O10(OH)2 ] Crystal: Monoclinic Pt. Group: 2/m Habit: platy SG: 2.8; H: 2 to 2.5 L: vitreous to pearly; Str: white Col: brown, green, reddish-brown Clev: perfect [001] Optics: Biaxial (-); bir=0.028-0.045 nα=1.53; nβ=1.557, nγ=1.558

Name Derivation: From the Greek flogopos - "resembling fire."

http://cache.eb.com/eb/image?id=9648&rendTypeId=4


Occurrence: Ultramafic Ig; Meta carbonates

Lepidolite (biotite series)

[K(Li,Al)2-3AlSi3O10(OH)2 ] Crystal: Monoclinic Pt. Group: 2/m Habit: platy SG: 2.84; H: 2.5-3 L: vitreous to pearly; Str: white Col: lilac (yellowish) to colourless Clev: perfect [001] Optics: Biaxial (-); bir=0.029-0.038 nα=1.525; nβ=1.551, nγ=1.554

Name Derivation: From the Greek lepidion - "scale"

http://webmineral.com/specimens/picshow.php?id=671


Occurrence: Li-bearing pegmatites

Margarite [CaAl2Al2Si2O10(OH)2 ]

Crystal: Monoclinic Pt. Group: 2/m Habit: scaly, massive SG: 3.03; H: 4 L: pearly; Str: white Col: white, grey (pinkish) Clev: good [001] Optics: Biaxial (-); bir=0.012-0.032 nα=1.595; nβ=1.625, nγ=1.627

From the Greek margaritos - "pearl."

http://webmineral.com/specimens/picshow.php?id=671


Occurrence: alteration product associated with corundum

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

Crystal: Monoclinic Pt. Group: 2/m Habit: scaly, massive SG: 2.65; H: 2 to 2.5 L: vitreous to 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

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

Phyllosilicate Minerals (interlayered)

http://itc.gsw.edu/faculty/tweiland/chlorit.jpg

Occurrence: Low grade metamorphosed mafic rocks, burial-grade sedimentary diagenesis

Talc (Talc Group) [Mg3Si4O10(OH)2]

Crystal: Monoclinic Pt. Group: 2/m Habit: scaly, massive SG: 2.75; H: 1 L: vitreous to pearly; Str: white Col: any colour, including smurf Clev: perfect [001] Optics: Biaxial (-); bir=0.037-0.050 nα=1.538; nβ=1.575, nγ=1.575

From the Arabian “talcia” meaning keep baby’s ass dry

Phyllosilicate Minerals (2:1 layers)

http://www.soes.soton.ac.uk/resources/collection/minerals/minerals

Occurrence: hydrothermal metamorphism

Pyrophyllite Al2Si4O10(OH)2

Crystal: Triclinic Pt. Group: 1 Habit: massive, acicular SG: 2.75; H: 1.5 to 2 L: pearly; Str: white Col: brown, grey, green, white Clev: perfect [001] Optics: Biaxial (-); bir=0.045-0.062 nα=1.534; nβ=1.586, nγ=1.596

Phyllosilicate Minerals (talc group; 2:1 layers)

http://www.mindat.org/photo-60228.html

Occurrence: hydrothermal metamorphic veins

From the Greek pyr - "fire" and phyllon – “leaf”

GY 302: Crystallography and Mineralogy

Lecture 23: Silicates 6: Micas

Instructor: Dr. Doug Haywick [email protected]

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

For personal use only.

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Mineral Quizzes Results - University of South Alabama