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Chamosite is a member of the Chlorite, and it forms a series with the mineral Clinochlore.
Chamosite is the iron rich end member, and Clinochlore is the
magnesium-rich end member. Their properties are very similar, and they are difficult to distinguish from each other, though Chamosite is harder, heavier, and usually less transparent than Clinochlore. |
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Chemical Formula |
(Fe2+,Mg)5Al2Si3O10(OH)8 |
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Composition |
Basic magnesium iron aluminum silicate. |
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Color |
Greenish-gray, gray, greenish-black, brown |
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Streak |
White |
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Hardness |
2.5 - 3 |
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Crystal System |
Monoclinic |
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Crystal Forms
and Aggregates |
Crystals, which are usually very small, are tabular and pseudohexagonal in shape, but
also may be prismatic. Also in
foliated, flaky, scaly, and rosette forms. May also be massive, radiating, and globular
masses of dense flakes. |
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Transparency |
Translucent |
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Specific Gravity |
3 - 3.4 |
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Luster |
Vitreous to pearly |
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Cleavage |
1,1 |
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Fracture |
Uneven |
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Tenacity |
Thin flakes are flexible but not elastic. |
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Other ID Marks |
Larger crystals and masses may have a slightly greasy feel. |
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In Group |
Silicates; Phyllosilicates; Chlorite Group |
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Striking Features |
Color and lack of elasticity |
| Environment |
As an alteration mineral of metamorphic iron deposits, but also as a secondary mineral in igneous traprock environments and granite pegmatites.
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| Rock Type |
Igneous, Metamorphic |
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Popularity (1-4)
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3 |
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Prevalence (1-3)
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2 |
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Demand (1-3) |
3 |
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Chamosite is more common then perceived, but it usually is just in small uninteresting flakes labelled as Chlorite without being specifically identified. Specific occurences include the Yaogangxian Mine, Hunan Province, China; Klenovec, Slovakia; Ashland, Middlesex Co., Massachusetts; Washington Pass, Okanogan Co., Washington; Atlantic City, Fremont Co., Wyoming; and Moat Mountain, Carroll County, New Hampshire. The New Jersey traprock quarries of Paterson and Prospect Park, Passaic Co., and the Milington Quarry, Somerset Co. contain Chamosite coatings and dustings upon other minerals.
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Muscovite and other micas - Are more elastic then Chlorites.
Talc - Softer (1).
Other Chlorite minerals - Indistinguishable by practical methods.
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