Cryptomelane

Formula:  K(Mn,MN)8O16

Origin of name:  From Greek for concealed and black

 

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:  On {010} or {10-1}, yielding pseudo-tetragonal cell

Unit cell: a = 8.31 Å, b = 2.88 Å, c = 9.94 Å, β = 90.6°

 

Colour:  Steel-grey to bluish grey to dull black

Diaphaneity:  Opaque

Luster:  Metallic, submetallic or dull

Habit:  Massive, fine-grained, botryoidal, radial-fibrous to distinct fibres

Hardness:  6 to 6.5

Specific gravity:  4.36

Cleavage:  None

Tenacity:

Streak:  Brownish black

 

Synonyms/varieties:

 

Comments:

 

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