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Category Carbonate mineral
(repeating unit)
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
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 [1][2][3]

Gregoryite is an anhydrous carbonate mineral that is rich in potassium and sodium[4] with formula: [(Na2,K2,Ca)CO3].[1][5][6] It is one of the two main ingredients of natrocarbonatite, found naturally in the lava of Ol Doinyo Lengai volcano, the other being nyerereite.[7]

Because of its anhydrous nature, gregoryite reacts quickly with the environment, causing the dark lava to be converted to white substance within hours.[4]

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.[1][2] It occurs associated with nyerereite, alabandite, halite, sylvite, fluorite and calcite.[3]


  1. ^ a b c
  2. ^ a b
  3. ^ a b Handbook of Mineralogy
  4. ^ a b "Gregoryite definition". Dictionary of Geology. Retrieved 2011-05-21. 
  5. ^ Mitchell, Roger H.; Bruce A. Kjarsgaard (2010). "Experimental Studies of the System Na2CO3–CaCO3–MgF2 at 0·1 GPa: Implications for the Differentiation and Low-temperature Crystallization of Natrocarbonatite". Journal of Petrology. Oxford Journals. 52 (7–8): 1265–1280. doi:10.1093/petrology/egq069. Retrieved 2011-05-21. 
  6. ^ Hay, Richard L (1989). "Holocene carbonatite-nephelinite tephra deposits of Oldoinyo Lengai, Tanzania". Journal of Volcanology and Geothermal Research. Elsevier (Netherlands). 37 (1): 77–91. Bibcode:1989JVGR...37...77H. doi:10.1016/0377-0273(89)90114-5. Retrieved 2011-05-21. 
  7. ^ "World's Coolest Lava is in Africa". Volcano Watch. "USGS Hawaiian Volcano Watch". Retrieved 2011-05-21.