Gregoryite

Gregoryite
Gregoryite
General
Category	Carbonate mineral
Formula; (repeating unit)	(Na2,K2,Ca)CO3
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

Gregoryite is an anhydrous carbonate mineral that is rich in potassium and sodium^[4] with the chemical 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]

References[]

^ ^a ^b ^c Mindat.org
^ ^a ^b Webmineral.com
^ ^a ^b Handbook of Mineralogy
^ ^a ^b "Gregoryite definition". Dictionary of Geology. Retrieved 2011-05-21.
^ 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.
^ 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.^{[dead link]}
^ "World's Coolest Lava is in Africa". Volcano Watch. USGS Hawaiian Volcano Watch. Retrieved 2011-05-21.

[mindat-1] Mindat.org

[Webmin-2] Webmineral.com

[HBM-3] Handbook of Mineralogy

[GeologyDictionary-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.

[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.^{[dead link]}

[7] "World's Coolest Lava is in Africa". Volcano Watch. USGS Hawaiian Volcano Watch. Retrieved 2011-05-21.

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