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Category Carbonate mineral
(repeating unit)
Strunz classification 05.AA.10
Crystal symmetry Hexagonal dihexagonal pyramidal
H-M symbol: (6mm)
Space group: P 63mc
Unit cell a = 5.21 Å, c = 6.58 Å; Z=2
Color Brown, milky white
Crystal habit Phenocrysts in carbonatite lava
Crystal system Hexagonal
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.