Chemical Formula |
Al2SiO5 |
Composition |
Aluminum silicate |
Color |
Light to dark blue, indigo-blue. Sometimes multicolored with different shades of blue or white, or with color streaks or stripes. A frequent habit is a deeper colored blue streak running through the center of a crystal. Less commonly colorless, white, gray, green, orange, or black. |
Streak |
Colorless |
Hardness |
4.5 - 7 |
Crystal System |
Triclinic |
Crystal Forms |
Most often in long and slender bladed crystals. Also in bladed crystal groups, radiating, in veins,reticulated, and in flattened tabular crystals. Rarely twinned in v-shaped butterfly twins. |
Transparency |
Transparent to translucent |
Specific Gravity |
3.5 - 3.7 |
Luster |
Vitreous |
Cleavage |
1,1;2,1 |
Fracture |
Splintery |
Tenacity |
Brittle |
In Group |
Silicates; Nesosilicates |
Striking Features |
Different direction hardness and color. |
Environment |
In metamorphosed schists and gneisses. Also in granite pegmatites. |
Rock Type |
Igneous, Metamorphic |
Popularity (1-4) |
2 |
Prevalence (1-3) |
2 |
Demand (1-3) |
2 |
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