Gregoryite

Gregoryite is an anhydrous carbonate mineral that is rich in potassium and sodium^[5] with the chemical formula (Na₂,K₂,Ca)CO₃.^[2][6][7] It is one of the two main ingredients of natrocarbonatite, found naturally in the lava of Ol Doinyo Lengai volcano of Arusha Region, Tanzania, and the other being nyerereite.^[8]

Gregoryite
General
Category	Carbonate mineral
Formula	(Na2,K2,Ca)CO3
IMA symbol	Ggy[1]
Strunz classification	5.AA.10
Crystal system	Hexagonal
Crystal class	Dihexagonal pyramidal (6mm) (same H-M symbol)
Space group	P63mc
Unit cell	a = 5.21 c = 6.58 [Å]; Z = 2
Identification
Color	Brown, milky white
Crystal habit	Phenocrysts in carbonatite lava
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.27 (calculated)
Optical properties	Uniaxial
Solubility	Soluble in water
References	[2][3][4]

Because of its anhydrous nature, gregoryite reacts quickly with the environment, causing the dark lava to be converted to white substance within hours.^[5]

Gregoryite was first described in 1980 and named after the British geologist and author John Walter Gregory (1864–1932), who studied the East African Rift Valley.^[2][3] It occurs associated with nyerereite, alabandite, halite, sylvite, fluorite and calcite.^[4]