Cumengéite

Formula:  Pb₂₁Cu₂₀Cl₄₂(OH)₄₀

Origin of name:  For E. Cumenge, French mining engineer

Crystal system:  Tetragonal

Crystal class:  4/m 2/m 2/m

Twinning:

Unit cell: a = 15.10 Å, c = 24.52 Å

Colour:  Indigo-blue

Diaphaneity:

Luster:  Weakly vitreous

Habit:  Crystals octahedral or cubo-octahedral; parallel overgrowths on boléite and pseudoboléite

Hardness:  2.5

Specific gravity:  4.70

Cleavage:  3; {100} good, {110} distinct, {001} poor

Tenacity:

Streak:  Sky blue

Synonyms/varieties:

Comments: