Annite is a phyllosilicate mineral in the mica family. It has a chemical formula of KFe32+AlSi3O10(OH,F)2. Annite is the iron end member of the biotite mica group, the iron rich analogue of magnesium rich phlogopite. Annite is monoclinic and contains tabular crystals and cleavage fragments with pseudohexagonal outlines. There are contact twins with composition surface {001} and twin axis {310}.
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| - Annite is a phyllosilicate mineral in the mica family. It has a chemical formula of KFe32+AlSi3O10(OH,F)2. Annite is the iron end member of the biotite mica group, the iron rich analogue of magnesium rich phlogopite. Annite is monoclinic and contains tabular crystals and cleavage fragments with pseudohexagonal outlines. There are contact twins with composition surface {001} and twin axis {310}.
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sameAs
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dcterms:subject
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Category
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opticalprop
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diaphaniety
| - translucent to transparent
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mohs
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Other
| - diagnostic: occurrence: in magnesium poor igneous and metamorphic rocks.
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Gravity
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Name
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symmetry
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Caption
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dbkwik:geology/pro...iPageUsesTemplate
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molecular weight
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2V
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streak
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formula
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System
| - Monoclinic, pseudohexagonal
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pleochroism
| - X = brown; Y = Z = dark brown
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strunz
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Color
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unit cell
| - a = 5.39 Å, b = 9.33 Å, c = 10.29 Å; β = 100°; Z = 2
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tenacity
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cleavage
| - perfect in one direction {001}
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habit
| - usually in "blocks" of thin sheets or as aggregations of foliated thin scales. Includes large, well formed pseudohexagonal prisms up to 12 cm across and 15 cm long.
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twinning
| - contact twins with composition surface on {001} and twin axis {310}
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fracture
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refractive
| - nα = 1.625 - 1.631 nβ = 1.690 nγ = 1.691 - 1.697
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luster
| - submetallic to vitreous; pearly on cleavage surfaces
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abstract
| - Annite is a phyllosilicate mineral in the mica family. It has a chemical formula of KFe32+AlSi3O10(OH,F)2. Annite is the iron end member of the biotite mica group, the iron rich analogue of magnesium rich phlogopite. Annite is monoclinic and contains tabular crystals and cleavage fragments with pseudohexagonal outlines. There are contact twins with composition surface {001} and twin axis {310}. Annite was first described in 1868 for the first noted occurrence in Cape Ann, Rockport, Essex County, Massachusetts, US. It also occurs on Pikes Peak, El Paso County, Colorado. It occurs in igneous and metamorphic rocks that are deficient in magnesium. It occurs associated with fluorite and zircon in the type locality.
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