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Dr. Mac Culloch on Quartz Rock.
from the transparent quartz grains with which it is intimately united in the fresh rock.
- The same rock in point of external aspect, but evidently formed of highly compacted and rounded grains of many different colours. from the same place.
- Brown quartz rock, of which the fracture is so little granular that it almost approaches to common quartz; semitransparent. From the mountains of Mar, Angus, and elsewhere, alternating with, micaceous schistus.
- The same rock, in the same situations, of various shades of red.
- An almost equal granular mixture of pure transparent quartz, and snow-white felspar, the grains amorphous. From Arisaig and Balahulish, with micaceous schistus.
- The same, but with fragments of felspar, hearing obscure marks of crystallization. From the latter place.
- Waxy and perfectly compact quartz, having a porphyritic aspect from imbedded fragments of felspar; accompanying the same rocks.
- White granular quartz rock of a moderately fine grain, containing at the same time large angular pieces of quartz, of a diameter from half an inch to many inches. In the same series at Balahulish.
- White granular rock consisting of felspar and quartz traversed by veins of pure white granular quartz, resembling in colour and texture the finest sugar. From Jura, and elsewhere.
- Distinctly rounded grains of the purest transparent quartz and imbedded in a mass of very fine grained white quartz. From the Cape of Good Hope.
- An uniform mixture of grains of transparent white quartz and opaque reddish felspar, containing rounded pebbles and fragments
