X-ray Study of Psilomelane and Cryptomelane

Bibhuti Mukherjee
Geological Survey of India, Calcutta

Summary: Psilomelane has been shown to be orthorhombic with a 8·254, b 13·40, c 2·864 Å. by the application of Lipson's method. The indexing of powder photographs of psilomelane (R2″Mn8ivO16(OH)4, where R″ includes the bivalent metals Mn, Ba, Ca, Mg, Co) indicates the space-group P21212 (D23 with one molecule per unit cell. Indexing of powder photographs of psilomelane is not satisfactory with Vaux's axes. Fermor's ‘psilomelane’ is cryptomelane, which is tetragonal with a 9·822, c 2·858 Å. Cryptomelane (KR8O16, where R stands for Mn in different valency states, partly replaced by other cations) is body-centred tetragonal with one molecule per unit cell. Fermor's stalactitic ‘psilomelane’ has an inner dull core of cryptomelane and an outer fine-grained crust of pyrolusite in each needle-shaped body.

Mineralogical Magazine; July 1959 v. 32; no. 245; p. 166-171; DOI: 10.1180/minmag.1959.32.245.08
© 1959, The Mineralogical Society
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