Voltaite

Formula: K₂Fe₅Fe₄(SO₄)₁₂.18H₂O

Origin of name: for Count Alessandro Giuseppe Antonio Anastasio Volta (1745-1827), Italian physicist and pioneer in electricity.

Crystal system: Cubic/Isometric

Crystal class: 4/m 3 2/m

Twinning:

Unit cell: a = 27.178

Colour: Dark olive-green, dark green, greenish black to black

Diaphaneity: Opaque, translucent in thin splinters

Luster: Resinous

Habit: Crystals octahedral and dodecahedral, massive, granular

Hardness: 3

Specific gravity: 2.6-2.8

Cleavage: None

Tenacity: Uneven to conchoidal fracture

Streak: Grayish green

Synonyms/varieties:

Comments:  Soluble in water, yielding an acid solution and citron-yellow residue