Zinnwaldite

Formula: KLiFeAl(AlSi3)O10(F,OH)2

Origin of name: locality Zinnwald, Czech Republic

 

Crystal system: monoclinic

Crystal class: 2/m

Twinning:

Unit cell: a = 5.27 Å, b = 9.187 Å, c = 20.02 Å, β = 101°

 

Colour: Gray, brown, dark green

Diaphaneity: Transparent

Luster: Vitreous, pearly on cleavage

Habit: Crystals short prismatic or tabular; scaly aggregates or disseminated scales, micaceous, pseudo-hexagonal

Hardness: 2.5 to 4

Specific gravity: 2.9 to 3.3

Cleavage: 1; {001} perfect, micaceous

Tenacity: Uneven fracture

Streak: White

 

Synonyms/varieties:

 

Comments:

 

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