Cymrite

silicate

amphibolite facies

Formula: Ba(Si,Al)4(O,OH)8.H2O
Unclassified silicate
Specific gravity: 3.41
Hardness: 2 to 3
Streak: White
Colour: White, colourless, green or brown. Green and brown colours are caused by inclusions of alteration products (Mindat).
Solubility: Slightly soluble in acids
Environments:

Metamorphic environments

Cymrite occurs in bedded manganese ore deposits due to low to medium grade metamorphism, amphibolite facies. It is stable at high pressure (Dana).

At the Andros Islad, Greece, cymrite is a product of high-pressure metamorphism of manganese-rich rocks (HOM).

At Långban, Sweden, cymrite is associated with hyalotekite, banalsite, hyalophane, hedyphane and manganoan biotite (HOM).

At the Benallt mine, Wales, UK, cymrite occurs in veinlets cutting hydrothermal manganese silicate ore, associated with ganophyllite (AM35.135).

At Ruby Creek in the Cosmos Hills, Brooks Range, Alaska, USA, cymrite occurs as minute crystals randomly scattered throughout a fine-grained dolomitic and sideritic matrix. The host-rock was originally a normal dolomite of marine origin, but it is now mineralised and contains pyrite, chalcopyrite, bornite, chalcocite, sphalerite, galena and cymrite, together with small amounts of chlorite, fluorite, pyrrhotite, dickite, and bementite. Cymrite is observed in contact with one or more of the following minerals: dolomite, siderite, ankerite, pyrite, fluorite, quartz and chlorite. (AM49.158).

At San Benito county, California, USA, cymrite occurs in jadeite greywacke (a dark coarse-grained sandstone containing more than 15 per cent clay) near the contact of an intrusive ultramafic rock, associated with calcite, albite and lawsonite.

Alteration

hydroxyl-poor cymrite to celsian and H2O
BaSi2Al2O8.H2O ⇌ Ba(Al2Si2O8) + H2O
Cymrite alters to celsian by dehydration.

Common impurities: Ti,Fe,Mn,Na,K

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