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Muscovite - Biotite (mixture) aka gigantolite ps after Cordierite

#PD40418

Muscovite - Biotite (mixture) aka gigantolite ps after Cordierite

#PD40418
Availability
Sold
Size
6 x 5 x 6 cm - Sm Cabinet 
Formula
KAl2(Si3Al)O10(OH)2 (RRUFF)
Locality
Lemn‪äs, Kemiö Island, Finland
Tagged
pegmatite mineral

This is a weird one, one of which had been described in the old literature as "gigantolite" in reference to it huge, gigantic crystals once though to be a unique mineral. Later studies proved it to be only a mixture of micas. The old Excalibur and Heinrich label indicates that it is a variety of topaz, which evidently it is not.

Muscovite

Formula
KAl2(Si3Al)O10(OH)2 
Crystal System
Monoclinic 
Crystal Habit
Massive - Lamellar, Foliated, Micaceous 
Cleavage
Perfect, None, None 
Luster
Vitreous (Glassy) 
Color
white, gray, silver white, brownish white, greenish white 
Streak
white 
Class
Monoclinic - Prismatic 
Fracture
Brittle - Sectile 
Hardness
2-2.5 

Data courtesy of Webmineral.

Collection
Phillips Collection
Mineralpedia
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On Dakota Matrix
Previously Sold Muscovite
On Dakota Matrix
Other Available Muscovite
WebMineral
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Mindat
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