Gregoryite

{{Short description|Anhydrous carbonate mineral that is rich in potassium and sodium}}

{{Infobox mineral

| name = Gregoryite

| image = Gregorite.JPG

| alt =

| caption =

| category = Carbonate mineral

| formula = {{chem2|(Na2,K2,Ca)CO3}}

| IMAsymbol = Ggy{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}

| strunz = 5.AA.10

| system = Hexagonal

| class = Dihexagonal pyramidal (6mm)
(same H-M symbol)

| symmetry = P6₃mc

| unit cell = a = 5.21
c = 6.58 [Å]; Z = 2

| color = Brown, milky white

| habit = Phenocrysts in carbonatite lava

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| streak = White

| diaphaneity = Transparent to translucent

| gravity = 2.27 (calculated)

| density =

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| opticalprop = Uniaxial

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| solubility = Soluble in water

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| references = [http://www.mindat.org/min-6979.html Mindat.org][http://www.webmineral.com/data/Gregoryite.shtml Webmineral.com]{{Cite web |url=http://www.handbookofmineralogy.com/pdfs/gregoryite.pdf |title=Handbook of Mineralogy |access-date=2011-06-03 |archive-date=2019-05-08 |archive-url=https://web.archive.org/web/20190508113955/http://www.handbookofmineralogy.com/pdfs/gregoryite.pdf |url-status=dead }}

}}

Gregoryite is an anhydrous carbonate mineral that is rich in potassium and sodium{{cite web |url=http://www.theodora.com/geology/glossaryg.html#gregoryite |title=Gregoryite definition |work=Dictionary of Geology |accessdate=2011-05-21}} with the chemical formula {{chem2|(Na2,K2,Ca)CO3}}.{{Cite journal| last=Mitchell |first=Roger H. |author2=Bruce A. Kjarsgaard |title=Experimental Studies of the System Na₂CO₃–CaCO₃–MgF₂ at 0·1 GPa: Implications for the Differentiation and Low-temperature Crystallization of Natrocarbonatite |journal=Journal of Petrology |publisher=Oxford Journals |year=2010 | doi = 10.1093/petrology/egq069| volume=52| issue=7–8| pages=1265–1280|doi-access=free }}{{Cite journal| last=Hay |first=Richard L |title=Holocene carbonatite-nephelinite tephra deposits of Oldoinyo Lengai, Tanzania |journal=Journal of Volcanology and Geothermal Research |volume=37 |issue=1 |pages=77–91 |publisher=Elsevier (Netherlands) |year=1989| doi=10.1016/0377-0273(89)90114-5|bibcode = 1989JVGR...37...77H }}{{dead link|date=March 2019|bot=medic}}{{cbignore|bot=medic}} 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.{{cite web |url=http://hvo.wr.usgs.gov/volcanowatch/2003/03_04_17.html |title=World's Coolest Lava is in Africa |work=Volcano Watch |publisher=USGS Hawaiian Volcano Watch |accessdate=2011-05-21}}

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

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. It occurs associated with nyerereite, alabandite, halite, sylvite, fluorite and calcite.