PPL Staurolite garnet muscovite schist. Glen Lethnot Grit Formation, Water of Saughs, Glen Lethnot, Tayside Region. NO4339 7355. Collected B. Young, 2008. Staurolite in pleochroic yellows and a garnet (top right). The garnet is 1.2mm wide (left to right).
      The hand specimen below shows porphyroblasts of staurolite, reddish brown in hand specimen, but yellowish in thin section; they are not garnets. Staurolite has its occasional characteristic cruciform twinning (seen left centre in the hand specimen).

XPL Crossed polars show staurolite and isotropic garnet in a matrix of mainly quartz (grey and white interference colours) and muscovite (tabular crystals with bright interference colours). The BGS lexicon describes the Glen Lethnot Grit Formation (Dalradian) as follows: mixed psammite, semipelite and pelite. Psammites typically gritty. Pelites include types rich in staurolite and muscovite, and some are also kyanite-bearing. Schists rich in iron-ore minerals form mappable units in places. Beds of quartzite with specks of green mica occur rarely near the base of the Formation. 

 The mineral is named after the Greek word stauros meaning cross. Staurolite occurs in regional metamorphic rocks rich in alumina and iron.


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