Delhayelite, a New Silicate from the Belgian Congo

Th. G. Sahama and Kai Hytönen
Institute of Geology, University of Helsinki, Finland.

Summary: The complex kalsilite-bearing melilite-nephelinite from Mt. Shaheru in the Belgian Congo with götzenite, combeite, and kirschsteinite contains yet another new silicate for which the name delhayelite is proposed.

Delhayelite is orthorhombic with a 6·53, b 24·65, c 7·04 Å. Possible space-groups Pmn21 and Pmmn. Weak super-cell with doubled a-axis. Distinct cleavage parallel to (010). Birefringence weak. αβγ = 1·532. 2Vα = 83°. Optical orientation: a = α, b = γ, c = β. Sp. gr. 2·60. Chemical composition corresponds to the tentative formula (Na,K)4Ca5Al6Si32O80.18H2O.3(Na2,K2)(Cl2,F2,SO4).

Mineralogical Magazine; March 1959 v. 32; no. 244; p. 6-9; DOI: 10.1180/minmag.1959.032.244.02
© 1959, The Mineralogical Society
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