Noun
A mineral related to ottrelite.
Clay slate; argillaceous schist.
Source: Webster's dictionaryBetween convert, the North Col Formation consists chiefly of biotite-quartz phyllite and chlorite-biotite phyllite intercalated with minor amounts of biotite- sericite -quartz schist. Source: Internet
The remainder of the North Col Formation, exposed between convert on Mount Everest, consists of interlayered and deformed schist, phyllite, and minor marble. Source: Internet