Bunsenite is the naturally occurring form of nickel(II) oxide, NiO. It occurs as rare dark green crystal coatings. It crystallizes in the cubic crystal system and occurs as well formed cubic, octahedral and dodecahedral crystals. It is a member of the periclase group.

Bunsenite
Bunsenite with unknown colorless crystals from the collection of the „Verein zur Förderung der Lithothek“, Munich (collection number A022658). Field of view 1 mm. Locality: Kochhütte, Helbra, Mansfeld-Südharz, Saxony-Anhalt, Germany
General
Category	Oxide mineral
Formula (repeating unit)	NiO
IMA symbol	Bus[1]
Strunz classification	4.AB.25
Crystal system	Cubic
Crystal class	Hexoctahedral (m3m) H–M symbol: (4/m 3 2/m)
Space group	Fm3m
Unit cell	a = 4.1769 Å; Z = 4
Identification
Color	Dark pistachio-green
Crystal habit	Octahedral crystal coatings, also cube or dodecahedron forms
Twinning	Observed
Cleavage	None
Mohs scale hardness	5.5
Luster	Vitreous
Streak	Brownish-black
Diaphaneity	Transparent
Specific gravity	6.898
Optical properties	Isotropic
Refractive index	n = 2.37
Other characteristics	Very high relief
References	[2][3][4][5]

It was first described in 1868 for a sample from a hydrothermal nickel–uranium vein from Johanngeorgenstadt, Ore Mountains, Saxony, Germany and named for German chemist Robert Bunsen (1811–1899).^[3][5] Other occurrences include west of the Scotia talc mine near Bon Accord, Barberton district, Transvaal, South Africa and from Kambalda south of Kalgoorlie, Western Australia. The South African occurrence has evidence of thermal metamorphism of a nickel-rich meteorite.^[4] It occurs associated with native bismuth, annabergite, aerugite, xanthiosite in Germany; and with liebenbergite, trevorite, nickeloan serpentine, nickeloan ludwigite, violarite, millerite, gaspeite, nimite and bonaccordite in the South African occurrence.^[4]