Carleton College, Department of Geology

Rocks and Minerals Study Guide

Orthosilicate Minerals

Name Image Color Hardness Streak Cleavage Luster Other properties

Forsterite
1, 2, 3, 4, 5

6, 7, 8, 9, 10

 green 6.5-7 colorless

is poor in two directions at 90 degrees,

is more distinct in fayalite

 vitreous Associated Minerals are diopside, spinel, plagioclase feldspars, chromite, hornblende, serpentine, iron-nickel meteorites and augite.
Fayalite

1, 2, 3, 4, 5

6, 7, 8, 9, 10

green
6.5-7
colorless

is poor in two directions at 90 degrees,

is more distinct in fayalite
vitreous
Associated Minerals are diopside, spinel, plagioclase feldspars, chromite, hornblende, serpentine, iron-nickel meteorites and augite.
Zicon

1, 2, 3, 4, 5

6, 7, 8, 9, 10
Brown, Reddish brown, Colorless, Gray, Green.
7.5
white
{110} Indistinct
Adamantine
Specific Gravity of Zircon =4.85 gm/cc.
Sphene

1, 2, 3, 4, 5

6, 7, 8, 9, 10

Reddish brown, Gray, Yellow, Green, Red.
5-5.5
redish white

{110} Distinct, {100} Imperfect,

{112} Imperfect
Adamantine
Crystalline - Fine - Occurs as well-formed fine sized crystals.
Pyrope

1, 2, 3, 4, 5

6, 7, 8, 9, 10

Typically dark red to red brown
6.5-7.5
white
none
vitreous
can be of gem quality
Almandine

1, 2, 3, 4, 5

6, 7, 8, 9, 10

Typically dark red to red brown
6.5-7.5
white
none
vitreous
can be of gem quality
Grassularite

1, 2, 3, 4, 5

6, 7, 8, 9, 10

Typically dark red to red brown
6.5-7.5
white
none
vitreous
can be of gem quality
Sillmanite

1, 2, 3, 4, 5

6, 7, 8, 9, 10
Bluish, Brownish greenish, Colorless, Gray, Gray green.
7.0
white
{010} Perfect
Vitreous
Occurs as needle-like crystals
Kyanite

1, 2, 3, 4, 5

6, 7, 8, 9, 10
Blue, White, Gray, Green, Black.
4-7
white
{100} Perfect, {010} Imperfect
Vitreous
Columnar - Forms columns
Andalusite

1, 2, 3, 4, 5

6, 7, 8, 9, 10
Dark green, Gray, Brown, Red, Green.
6.5-7
white

110} Distinct, {100} Indistinct,

{010} Poor
Vitreous
Occurs as well-formed crystals showing good external form
Staurolite

1, 2, 3, 4, 5

6, 7, 8, 9, 10
Brownish yellow, Brownish black, Yellow brown, Dark brown, Reddish brown.
7-7.5
gray
{010} Distinct
Vitreous
Twinning Common - Crystals are usually twinned.
Topaz

1, 2, 3, 4, 5

6, 7, 8, 9, 10
Colorless, Pale blue, Yellow, Yellowish brown, Red.
8
white
{001} Perfect
Vitreous
Prismatic - Crystals Shaped like Slender Prisms