Gregoryite

Gregoryite is an anhydrous carbonate mineral that is rich in potassium and sodium[4] with the chemical formula (Na
2,K
2,Ca)CO
3.[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]

Gregoryite
General
CategoryCarbonate mineral
Formula
(repeating unit)		(Na
2,K
2,Ca)CO
3
Strunz classification5.AA.10
Crystal systemHexagonal
Crystal classDihexagonal pyramidal (6mm)
(same H-M symbol)
Space groupP63mc
Unit cella = 5.21
c = 6.58 [Å]; Z = 2
Identification
ColorBrown, milky white
Crystal habitPhenocrysts in carbonatite lava
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.27 (calculated)
Optical propertiesUniaxial
SolubilitySoluble in water
References[1][2][3]

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]

References
  1. Mindat.org
  2. Webmineral.com
  3. Handbook of Mineralogy
  4. "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.
  7. "World's Coolest Lava is in Africa". Volcano Watch. USGS Hawaiian Volcano Watch. Retrieved 2011-05-21.
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