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Formula: Ba(Si,Al)4(O,OH)8.H2O
Unclassified silicate
Crystal System: Monoclinic
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
Common impurities: Ti,Fe,Mn,Na,K
Environments:
Cymrite occurs in bedded manganese ore deposits due to low to medium grade metamorphism,
amphibolite facies. It is stable at high pressure
(Dana).
Localities
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.
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