Under large areas of Otago and smaller areas of Marlborough lies schist, similar to the rock illustrated here from Queen Charlotte Sound. Schist is a metamorphic rock that has been deeply buried, heated and recrystallised, so that it breaks along a preferred direction (called the schistosity). During recrystallisation the minerals have often been segregated into dark and light layers. The light layers are made of quartz and feldspar, while the darker layers are mainly minerals such as chlorite and biotite.
Such layered or banded metamorphic rocks are usually called gneiss overseas – the term schist is a New Zealand peculiarity.
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Photograph by Lloyd Homer
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