Minrecordite

minerals

dioptase

malachite

duftite

Formula: CaZn(CO3)2
Anhydrous normal carbonate, dolomite group
Specific gravity: 3.45
Hardness: 3½ to 4
Streak: White
Colour: White, colourless
Solubility: Slowly dissolved by acids in cold, dilute hydrochloric acid, rapidly dissolved by warm acids (AM 68.280-283)
Environments

Hydrothermal environments

Minrecordite occurs in the oxidation zone as a secondary carbonate in carbonate-hosted zinc ores (Webmin).

Localities

At the Navan Mine, County Meath, Ireland, minrecordite occurs in the wallrock of a carbonate-hosted lead-zinc orebody associated with sphalerite, pyrite, marcasite, magnesian calcite, dolomite, calcite and quartz (HOM)

At the type locality, the Tsumeb Mine, Oshikoto Region, Namibia, minrecordite occurs in a dolostone-hosted hydrothermal polymetallic deposit (Mindat, HOM).
It is found on dioptase, and with zincian dolomite, duftite and malachite needles in the oxidation zone; manganese-rich minrecordite is also found here with ochre (earthy minerals) inclusions, and associated with cerussite and calcite (AM 68.42-45, Dana, HOM)

Alteration

Minrecordite forms at the type locality at low temperatures under oxidising conditions. Thermochemical calculations indicate that pure end member minrecordite would be unstable under ambient atmospheric conditions, and in nature some magnesium (from dolomite) remains unchanged, whilst most of it is replaced by zinc (AM 68.42-45, R&M 95.1.42-45)
The paragenetic sequenceis as follows:
1. calcite, zincian dolomite and duftite
2. dioptase I
3. magnesian minrecordite, rarely associated with cerussite and calcite
4. minrecordite
5. dioptase II
(Minrec 13.131-136)

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