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Stilpnomelane

A species of Minerals, Also known as Minguetite

Stilpnomelane is a phyllosilicate mineral. It has the formula K(Fe,Mg,Fe)8(Si,Al)12(O,OH)27·n(H2O). Stilpnomelane occurs associated with banded iron formations. It is a metamorphic mineral associated with the blueschist and greenschist facies. It was first described in 1827 for an occurrence in Moravia in the Czech Republic. The name is derived from the Greek stilpnos for shining, and melanos for black.

Hardness:

3 - 4

Density:

2.667 g/cm³

General Info About Stilpnomelane

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Physical Properties of Stilpnomelane

Colors

Red, brown, black, dark green, dark reddish brown, golden brown

Streak

White, grey

Hardness

3 - 4 , Soft

Density

2.667 g/cm³, Normal Weight

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Chemical Properties of Stilpnomelane

Formula

(K,Ca,Na)(Fe,Mg,Al)₈(Si,Al)₁₂(O,OH)₃₆ · nH₂O

The ratio of ferric vs. ferrous iron varies greatly. An ideal end-member "ferrostilpnomelane" can be represented by K₅Fe₄₈²⁺(Si₆₃Al₉)O₁₆₅(OH)₄₈.12H₂O. An ideal end-member "ferristilpnomelane" (which is thought to result from oxidation after primary crystallization) can be represented by K₅Fe₄₈³⁺(Si₆₃Al₉)O₂₁₆.36H₂O. Note that neither end-member composition has been reported yet.

Elements listed

Al, Ca, Fe, H, K, Mg, Na, O, Si

Common Impurities

Ti,Mn,Ca,Na,K,H₂O

Characteristics of Stilpnomelane

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