1. Ge 11a/101. Introduction to Geology and Geochemistry
Lecture 2
Crystal Structure of Minerals

2. Image 2.1

3. Image 2.2 Cleavage planes and number of cleavage directions Silicate
structure
Specimen
Mineral
Chemical formula
1 plane
Isolated
tetrahedra
Olivine
(Mg,Fe)2SiO4
2 planes at 90°
Single chains
Pyroxene
(Mg,Fe)SiO3
2 planes at 60°
and 120°
Double chains
Amphibole
Ca2(Mg, Fe)5Si8O22(OH)2
Sheets
1 plane
Muscovite:
KAl2(AlSi3O10)(OH)2
Micas
Biotite:
K(Mg, Fe)3AlSi3O10(OH)2
Three-dimensional
framework
2 planes at 90°
Orthoclase feldspar:
KAlSi3O8
Feldspars
Plagioclase feldspar:
(Ca, Na) AlSi3O8
Image 2.2