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Mica Schist

On the Dunalastair estate there is an exposure of Mica Schist which was considered for the commercial extraction of mica. The rock was bored and blasted to create extra exposures but in the final analysis it was decided that it was not economically viable.

There are two common forms of the mineral mica (a sheet silicate), namely, muscovite which is silvery and biotite which is black. The muscovite can have a variety of uses. It was used for furnace windows and in clothes irons as an insulator because it has a high melting point. Small crystals can be made into sheets for the windows and it was used for windows in early sports cars. It can also be used for Christmas card glitter and for anti-fouling paint for boats. In the sea, marine organisms often settle on the hulls of boats and ships and they become a drag on the vessel as it moves through the water. Anti-fouling paint helps to reduce this and in the case of those that make use of the mica it works because the mica flakes away from the hull and does not provide a secure fastening area for the organism.

The name muscovite comes from the City of Moscow where mica was used in windows. In Russia there are places where there are particularly large crystals.

The muscovite of the Dunalastair estate is in a small south facing cliff on the opposite side of the River Tummel from Schiehallion. When the sun shines the cliff faces glitters in an attractive manner.

The exposure also contains small crystals of pink garnet. Garnet is semi-precious but these crystals are too small and soft to be of gem quality. Garnet is hard (5 on Mohs scale of hardness) and garnet can be used as an abrasive - hence garnet paper which is a type of snadpaper.

Muscovite
Muscovite and Biotite
A bore hole used to balst the rock is visible at the top of the photo
There are small pink garnets here although they are not easily visble.
 
Mica Schist with lichens growing on the rock and gorse in the foreground.

Rannoch Net