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Lawsonite is a rare mineral, and is a hydrated variant of the feldspar Anorthite. It is named after Andrew Cowper Lawson (1861-1952), a professor of geology at the University of California at Berkeley. The Bay Area of California is the type locality and primary region of this mineral, and this is where Lawson taught. Lawson's main claim to fame is his identification and naming of the San Andreas Fault. |
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Chemical Formula |
CaAl2Si2O7(OH)2 · H2O |
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Composition |
Hydrous basic calcium aluminum silicate |
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Color |
Light blue, light pink, light purple, gray, tan, or white. May also be multicolored with color zoning of light blue, light pink, or light purple. Rarely bright green or bluish-green. |
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Streak |
White |
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Hardness |
7.5 |
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Crystal System |
Orthorhombic |
Crystal Forms
and Aggregates |
Crystals are usually prismatic or tabular, and they are often crude and of grainy appearance. Also in groupings of stubby or tabular crystals. May also be granular and massive. Crystals are sometimes twinned. |
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Transparency |
Transparent to translucent |
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Specific Gravity |
3.1 |
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Luster |
Vitreous |
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Cleavage |
1,2;3,3 |
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Fracture |
Uneven |
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Tenacity |
Brittle |
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In Group |
Silicates; Sorosilicates |
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Striking Features |
Localities, perfect cleavage, color, and hardness. |
| Environment |
In metamorphosed blue schists, as well as altered gabbros and basalt. |
| Rock Type |
Metamorphic |
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Popularity (1-4)
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3 |
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Prevalence (1-3)
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3 |
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Demand (1-3) |
3 |
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- A bright green, chromium-rich variety of Lawsonite, described from Syros Island, Greece.
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Lawsonite is used in geological studies to determine the formation and metamorphism of certain rock formations.
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Lawsonite is a not commonly represented in collections, though this mineral is probably more widespread than perceived. In the U.S., the only significant localities are in the Coast Ranges area of Central California. Large, pale blue crystals of Lawsonite were found at the type locality near the Reed Station in the Tiburon Peninsula, Marin Co., California. This locality has since been built over and is no longer in existence. Light tan and pink crystals have come from Valley Ford, Sonoma Co., California. A deep green, chromium-rich form of Lawsonite was reported as newly discovered material from Cape Marmari, Syros Island, Greece, in 2010. |
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Celestine - Much software, primarily a sedimentary mineral.
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