A new analysis of ephesite from the Postmasburg district, South Africa, shows that the lithium content is much higher than previously determined. Ephesite is a trioctahedral member of the margarite group with formula Na(LiAl2)(Al2Si2)O10(OH)2; lithium fills the vacant octahedral position as calcium is replaced by sodium. X-ray study shows it to be of the 2M1 type with a 5.120, b 8.853, c 19.303 A., β 95°5'. Replacements involved in bityite, the lithium-beryllium member of the group, are discussed.

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