Title: Lecture 20 (12/06/2006) Systematic Description of Minerals Part 4: Silicates II: Cyclosilicates, Inosilicates, Phyllosilicates and Tectosilicates
1Lecture 20 (12/06/2006)Systematic Description
of Minerals Part 4 Silicates II
Cyclosilicates, Inosilicates, Phyllosilicates and
Tectosilicates
2Silicate Mineral Classification(based on
arrangement of SiO4 tetrahedra)
3Cyclosilicates (Ring)
- x(SiO3) Unit Composition
- Hexagonal and Orthorhombic (pseudohexagonal)
symmetries most common - Forms silicate minerals with
- Moderate density(2.6-3.2) and hardness (7-8)
- Prismatic habits
- Poor cleavage
Beryl
4Common Cyclosilicates
- Beryl Be3Al2(Si6O18)
- Common accessory mineral in granite pegmatite
- Gem varieties Aquamarine, Emerald, Rose Beryl,
Golden Beryl
Cordierite (Mg,Fe)2Al4Si5O18nH20 Common mineral
in contact metamorphosed argillaceous
rocks Resembles quartz in appearance and
hardness (7-7.5)
Tourmaline (Na,Ca)(Li,Mg,Al)3(Al,Fe,Mn)6(BO3)3 (Si
6O18)(OH)4 Common accessory mineral in granite
pegmatite Characteristic striated prisms with
trigonal outline
watermelon tourmaline
5Inosilicates (Chain)
- x(SiO3) Unit Composition
- Single and double silicon tetrahedra chains
- Typically monoclinic and orthorhombic symmetry
- Single chains (Pyroxenes) develop 90 cleavage
- Double chains (Amphiboles) develop 120 cleavage
Amphibole Structure
Pyroxene Structure
6Pyroxenes (XYZ2O6 )X (M2) Na, Ca, Mn, Fe2,
Mg, Li Y (M1) Mn, Fe2, Mg, Fe3, Cr3 ,
Ti4Z (Tetrahedral site) - Al3, Si4
Clinopyroxenes
Orthopyroxenes
7Exsolution in Pyroxene
Exsolved comp Original comp
8Amphiboles (A0-1X2Y5Z8O22 (OH,F))A Na, KX
(M4) Na, Ca, Mn, Fe2, Mg, Li Y (M1-3) Mn,
Fe2, Mg, Fe3, Cr3 , Ti4Z (Tetrahedral site)
- Al3, Si4
9Common Types of Amphiboles
10Phyllosilicates (Sheet)
- x(Si2O5) Unit Composition
- Infinite sheets of silicon tetrahedra
- Strong single cleavage parallel to silicon sheets
Pyrophyllite
Muscovite
11Phyllosilicate StructuresAlternating Si
Tetrahedral and Octahedral layers bound by large
cations or weak electrostatic bonds
12Common Phyllosilicates
Kaolinite
Chrysotile
Antigorite
Talc
Pyrophyllite
Muscovite
Biotite
Chlorite
Lepidolite
13Tectosilicates (Framework)
- x(SiO2) Unit Composition
- 3-D framework of linked silicon tetrahedra
- Variable physical properties and symmetries
depending on linkage of framework groupings
14SiO2 Group
Quartz SiO2
Opal SiO2nH2O
15Feldspar Group
16Alkali Feldspars
Perthite (albite exsolution in microcline)
17Plagioclase Feldspars
Albite Twinning
Compositional Zoning (Oscillatory)
18Feldspathoids (Si-poor feldspars)
- Common in alkaline (Si-undersaturated) igneous
rocks -
- Leucite KAlSiO4
- Nepheline (Na,K)AlSiO4
-
- Sodalite Na8(AlSiO4)6Cl2
19Hydrous Tectosilicates
- Analcime (Scapolite Gp) NaAlSi2O6H2O
- Natrolite (Zeolite Gp) Na2Al2Si3O102H2O
- Heulandite (Zeolite Gp) CaAl2Si7O186H2O
- Stilbite (Zeolite Gp) NaCa2Al5Si13O3614H2O
20Next Lecture 12/11/06
-
- Introduction to X-ray Diffractometry
- Read Klein p. 309-321
- 12/13 Final Review Mineralogy Trivia