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Cymrite

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Cymrite
Cymrite (2.2 x 1.6 x 1.6 cm)
General
CategoryPhyllosilicate
Formula
(repeating unit)
BaAl2Si2(O,OH)8·(H2O)
IMA symbolCym[1]
Crystal systemMonoclinic
Crystal classDomatic (m)
(same H-M symbol)
Space groupPm
Unit cella = 5.32 Å, b = 36.6 Å,
c = 7.66 Å; β = 90°; Z = 2
Identification
ColorBrown, greenish, colorless
Crystal habitMicacious, sheet-like, pseudohexagonal, also fibrous
CleavagePerfect on {001}, good on {110}
FractureUneven
TenacityBrittle
Mohs scale hardness2-3
LusterSilky, Vitreous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity3.49
Optical propertiesBiaxial (-)
Refractive indexnα = 1.611 nβ = 1.619 nγ = 1.621
Birefringenceδ = 0.010
2V angle0-5°
References[2][3][4][5][6][7]

Cymrite is a silicate mineral with the chemical formula BaAl2Si2(O,OH)8·H2O.[5] The mineral is named for Cymru, which is the Welsh word for Wales.[4]

Cymrite, with perfect cleavage and a monoclinic crystalline system, falls in the silicate group.[5] Silicates are formed of Silicon and Oxygen bonding together to form tetrahedra.[6] The symmetry of Cymrite is classified as having a mirror plane. It has a moderate relief, meaning the contrast between the mineral and the epoxy of a thin section makes cymrite easily visible. The birefringence of the mineral is 0.01.[5] Cymrite, being monoclinic is anisotropic with two optic axes.

Occurrence

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Cymrite was discovered in Wales but is found in other areas throughout the United States, Africa, Greece and other parts of Europe. It occurs in generally high temperature-pressure areas such as the hydrothermal manganese silicate ore that makes up the Benalt Mine in Wales and in manganese rock that has undergone high-pressure metamorphism found in Greece.[2] It is important to geologists because of its limited occurrence, when cymrite is present on a rock it indicates that the rock, at some point, must have experienced high pressure and temperature.

References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b Handbook of Mineralogy. Accessed October 15, 2010.
  3. ^ www.museumwales.ac.uk http://www.museumwales.ac.uk/en/mineralogy/database/?mineral=209. Retrieved October 2, 2010. {{cite web}}: Missing or empty |title= (help)[title missing]
  4. ^ a b Webmineral data Accessed September 5, 2010
  5. ^ a b c d Mindat.org. Accessed September 27, 2010
  6. ^ a b [O'Donoghue,M. (1976) The Encyclopedia of Minerals and Gemstones. Orbis Publishing, London].
  7. ^ Mineralienatlas