Nyerereite is a very rare sodium calcium

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

with formula Na₂ Ca( C O₃)₂. It forms colorless, platey pseudohexagonal

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with ...

crystals that are typically twinned. It has a

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its dens ...

of 2.54 and indices of refraction of nα=1.511, nβ=1.533 and nγ=1.535. Nyerereite is not stable in contact with the atmosphere and rapidly breaks down. Collection specimens must be kept in a sealed

argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice a ...

environment. It has a

Hermann–Mauguin notation In geometry, Hermann–Mauguin notation is used to represent the symmetry elements in point groups, plane groups and space groups. It is named after the German crystallographer Carl Hermann (who introduced it in 1928) and the French mineralogis ...

of mm2 and the respective space group is Cmc21. In nature Nyerereite is naturally twinned and is pseudohexagonal with triad twinning; meaning that this is a six sided crystal that apparently has a

hexagonal In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A '' regular hexagon'' has ...

shape but is not in the hexagonal system. Triad twinning is the intergrowth of three

crystals that turn at their center and form hexagonally shaped crystals. Nyerereite is biaxial negative, and has a 2v of 29 degrees. It shows a center acute

bisectrix In geometry, bisection is the division of something into two equal or congruent parts, usually by a line, which is then called a ''bisector''. The most often considered types of bisectors are the ''segment bisector'' (a line that passes through ...

and a birefringence of approximately 0.023.Mckie, D., Frankis, E.J., (1976) Nyerereite: A new volcanic carbonate mineral from Ol Doinyo Lengai, Tanzania. Zeitschrift für Kristallographie 145, 73-95 At high temperatures or just erupted lava nyerereite is uniaxial and shows an interference color of second order blue when twinning is not present, and when twinning is there the interference color of nyerereite is first order grey.

Special characteristics

Since nyerereite is very unstable when it reaches the surface it creates

pseudomorph In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form ( crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced ...

s, which is basically the process by which the rock appearance and dimensions remain constant but the main mineral component is replaced by another. McKie (1976) categorized nyerereite into two different categories, high and low nyerereite. There are two types because the

Ol Doinyo Lengai Ol Doinyo Lengai (Oldoinyo Lengai), "Mountain of God" in the Maasai language, is an active volcano located in the Gregory Rift, south of Lake Natron within the Arusha Region of Tanzania, Africa. Part of the volcanic system of the East African Ri ...

lavas are very soluble and hygroscopic; when they come in contact with water or the atmosphere, the lava changes physically and chemically. Therefore, when nyerereite is at high temperature or warm we have what McKie (1976) calls high nyerereite, but when it cools down and gets hydrated we have pirssonite that has a chemical formula of Na₂Ca(CO₃)₂·2(H₂O).

Occurrence and discovery

It was first recognized and described by J.B. Dawson from the

carbonatite Carbonatite () is a type of intrusive or extrusive igneous rock defined by mineralogic composition consisting of greater than 50% carbonate minerals. Carbonatites may be confused with marble and may require geochemical verification. Carbonati ...

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...

s in 1963 and named in honor of the president of

Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...

Julius Nyerere Julius Kambarage Nyerere (; 13 April 1922 – 14 October 1999) was a Tanzanian anti-colonial activist, politician, and political theorist. He governed Tanganyika as prime minister from 1961 to 1962 and then as president from 1962 to 1964, af ...

(1922-1999). In the carbonatite lava it is associated with the potassium-bearing gregoryite. It has also been reported from the Afrikanda alkaline intrusive complex, in the

Kola Peninsula The Kola Peninsula (russian: Кольский полуостров, Kolsky poluostrov; sjd, Куэлнэгк нёа̄ррк) is a peninsula in the extreme northwest of Russia, and one of the largest peninsulas of Europe. Constituting the bulk ...

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...

. Anatoly N Zaitsev and Anton R Chakhmouradian, ''Calcite – amphibole – clinopyroxene rock from the Afrikanda Complex, Kola Peninsula, Russia: mineralogy and a possible link to carbonatites. II. Oxysalt minerals'', The Canadian Mineralogist 40 pp 103-120 (Abstract)

References

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Bibliography

*Dawson, J.B., (1962) The geology of Ol Doinyo Lengai. Bulletin of Volcanologique 24,348-387. *Simkin, T., (1994) Volcanoes of the world. Geoscience press. second edition, 20-35. Carbonate minerals Julius Nyerere Orthorhombic minerals Minerals in space group 36