(mineralogy) FeAl4Si2O10(OH)4 A micaceous mineral related to the brittle mica group; has both monoclinic and triclinic modifications, a gray to green color, and weakly pleochroic crystals.
Chloritoid
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(′klör·ə′toid)
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A hydrous iron aluminum silicate mineral with an ideal formula of Fe22+Al4O2(SiO4)2(OH)4. Chloritoid occurs as platy, black or dark green crystals, rarely more than a few millimeters in size. Its density ranges from 3.46 to 3.80 g/cm3, and its hardness on the Mohs scale is 6.5. See also Hardness scales.
Chloritoid is increasingly being recognized as a constituent in rocks that formed under high-pressure conditions. It is found in association with glaucophane in blueschist-facies metamorphic rocks, and with amphibole and pyroxene in eclogite-facies metamorphic rocks. These are rocks that formed under conditions thought to prevail at the base of the Earth's crust or in the mantle. Experimental studies of metamorphism of basalt under these conditions indicate the formation of chloritoid at pressures exceeding 2300 MPa (23 kbar) and at a temperature of 650°C (1200°F). In these high-pressure occurrences of chloritoid, the chloritoid is rich in magnesium, having a value of Mg/(Mg + Fe) ranging from 0.38 to 0.40. See also Metamorphic rocks.
| Wikipedia: Chloritoid |
Chloritoid is a silicate mineral of metamorphic origin. It is an iron magnesium manganese alumino-silicate hydroxide with formula: (Fe,Mg,Mn)2Al4Si2O10(OH)4. It occurs as greenish grey to black platy micaceous triclinic crystals and foliated masses. Its Mohs hardness is 6.5, unusually high for a platy mineral, and it has a
It was first described in 1837 from localities in the Ural Mountains region of Russia.
References
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- ottrelite (mineralogy)
- chloritoid schist (petrology)
- Porphyroblast (mineralogy and petrology)
- Epidote (mineralogy and petrology)
