Ge 101. Introduction to Geology and Geochemistry

Lecture 2 Crystal Structure of Minerals

Image 2.1

Mineral Chemical formula

Cleavage planesand number of

cleavage directionsSilicate

structure Specimen

1 plane Isolatedtetrahedra

2 planes at 90°Single chains

2 planes at 60°and 120° Double chains

1 planeSheets

Olivine

Pyroxene

Amphibole

Micas

Feldspars

2 planes at 90°Three-dimensional

framework

(Mg,Fe)2SiO4

(Mg,Fe)SiO3

Ca2(Mg, Fe)5Si8O22(OH)2

Muscovite:KAl2(AlSi3O10)(OH)2

Biotite:K(Mg, Fe)3AlSi3O10(OH)2

Orthoclase feldspar:KAlSi3O8

Plagioclase feldspar: (Ca, Na) AlSi3O8

Image 2.2