Summary A manganese pan near Birness contains grains of an optically uniaxial negative mineral near (Na 0·7 Ca 0·3 )Mn 7 O 14· 2·8H 2 O, giving an X-ray powder pattern similar to that of synthetic materials described as ‘manganous manganite’ and δ-MnO 2 . Material giving a similar pattern has been described from a natural occurrence in Canada, but no mineral name was assigned; the name birnessite is now proposed. The mineral is probably formed by air-oxidation of manganous oxides under alkaline conditions.
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Jones et al. (1956) studied this question.
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