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Formula: Na2Ca(CO3)2
Anhydrous carbonate, hexagonal paramorph of orthorhombic
nyerereite
Crystal System: Hexagonal
Specific gravity: 2.46 measured, 2.47 calculated
Hardness: 2
Colour: Colourless
Solubility: Readily soluble in warm water
Common impurities: K
Environments
Igneous environments
Hydrothermal environments
Localities
At the Venkatampalle kimberlite, Anantapur District, Andhra Pradesh, India, the upper thermal stability of
zemkorite is ~700 K, which is similar to shortite. Zemkorite may
have formed during the late stages of kimberlite genesis, possibly
as a result of metasomatism or by the breakdown of
metasomatic natrocarbonatitic minerals or glass that segregated on decompression melting in the upper mantle
(AM 87.1384-1389).
At the type locality, the Udachnaya open-pit mine (Udachnaya-Vostochnaya pipe; Udachnaya pipe), Daldyn, Mirninsky
District, Sakha, Russia, zemkorite is found as tabular grains, 0.1 to 0.5 mm across, in cores at depths of
400 to 450 m; it typically fills thin fractures in unaltered
kimberlite, along contacts between groundmass and
olivine xenoliths and xenocrysts; rarely as fan-shaped aggregates 34 mm
across in interstices among large olivine xenocrysts. Associated minerals
are shortite and, rarely, halite.
Zemkorite is postmagmatic and results from reworking of the
kimberlite by highly mineralised sodic solutions derived by
interaction of the Udachnaya pipe with subsurface brines from Lower Cambrian (543 to 518 million years ago) country
rocks
(AM 75.933-934).
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