Piypite

Formula: K₂Cu₂(SO₄)₂O

Origin of name: for B. Piyp, Russian vulcanologist

Crystal system: tetragonal

Crystal class: 4

Twinning: 

Unit cell: 

Colour: emerald-green to dark green to black

Diaphaneity: transparent

Luster: 

Habit: crystals acicular or columnar, 3 cm long, in aggregates

Hardness: 2.5

Specific gravity: 3.10

Cleavage: 1; perfect parallel to elongation

Tenacity: 

Streak: yellowish green

Synonyms/varieties:

Comments: unstable in air, decomposed by H₂O, readily soluble in dilute acids