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Welshite, Ca2Mg4Fe3+Sb5+O2[Si4Be2O18], a new member of the aenigmatite group

Published online by Cambridge University Press:  05 July 2018

Paul B. Moore
Paul B. Moore*
Affiliation:
Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois 60637, U.S.A.
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Summary

Welshite, triclinic, Ca2Mg4Fe3+Sb5+O2 [Si4Be2O18], a = 10·28 Å, b = 10·69 Å, c = 8·83 Å, α = 106·1°, β = 96·3°, γ = 124·8°, P¯1 with pseudo-monoclinic cell am = 9·68(1) Å, bm = 14·77(2) Å, cm = 5·14(1) Å, βm = 101·5(2)°, c-centred, occurs as lustrous subadaman-tine, thick prismatic reddish-black crystals up to 3 mm in greatest dimension associated with roméite, adelite, swedenborgite, berzeliite, manganoan phlogopite, richterite in crystalline dolomite from Làngban, Sweden. Forms include b {010}, a{100}, k{130}, m{110}, j{021}, p{111}, q{121}, v{131}, r{¯111}, s{¯121}, t{¯131}, and v{¯141} (monoclinic setting). Streak pale-brown, hardness 6, specific gravity 3·77, fracture conchoidal, no cleavage, α = 1·81(1), γ = 1·83(1), 2E(obs.) ≈45°, no noticcable pleochroism.

Welshite is a new member of the aenigmatite-rhönite group and obtains from the substitution Sb5+→ Ti4+ and Be2+ → Al3+ in rhönite.

Type
Research Article
Information
Mineralogical Magazine , Volume 42 , Issue 321 , March 1978 , pp. 129 - 132
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1978

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References

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Errata and Addenda