Piypite

Piypite is a rare potassium, copper sulfate mineral with formula: K₂Cu₂O(SO₄)₂. It crystallizes in the tetragonal system and occurs as needlelike crystals and masses. Individual crystals are square in cross-section and often hollow. It is emerald green to black in color with a vitreous to greasy luster.[3][4]

Piypite
Green acicular crystals of piypite
General
Category	Sulfate mineral
Formula (repeating unit)	K2Cu2O(SO4)2
IMA symbol	Piy[1]
Strunz classification	7.BC.40
Crystal system	Tetragonal
Crystal class	Pyramidal (4) H-M symbol: (4)
Space group	I4
Unit cell	a = 13.6 Å, c = 4.95 Å; Z = 2
Identification
Color	Emerald-green, dark green, black
Crystal habit	Acicular crystals elongated along [001], square cross section, commonly hollow; also as mosslike aggregates
Cleavage	Perfect, parallel to elongation
Tenacity	Brittle
Mohs scale hardness	2.5
Luster	Vitreous to greasy
Streak	Yellowish green
Diaphaneity	Transparent to translucent
Specific gravity	3.0 - 3.1
Optical properties	Uniaxial (+)
Refractive index	nω = 1.583 nε = 1.695
Birefringence	δ = 0.112
Pleochroism	Distinct; O = pale green, yellowish green; E = deep green, pale yellowish green
Solubility	Soluble in water, leaves residue
References	[2][3][4][5]

It was first described in 1982 for an occurrence in the Main Fracture of the Tolbachik volcano, Kamchatka Oblast, Russia. It has also been reported from Mount Vesuvius, Italy, and in a slag deposit in the Bad Ems District in the Rhineland-Palatinate, Germany.[3][2] Piypite occurs as a sublimate phase in a fumarole environment. Associated minerals include halite, sylvite, langbeinite, tenorite, hematite, tolbachite, dolerophanite, urusovite, aphthitalite, ponomarevite, cotunnite, chalcocyanite, sofiite, euchlorine, averievite, fedotovite, alarsite, alumoklyuchevskite, nabokoite and lammerite at the type locality in Kamchatka. On Vesuvius, it occurs with paratacamite.[3]