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Dr. Mac Culloch on Quartz Rock.
- White quartz, with a fracture almost purely splintery, the granular texture being invisible to the naked eye, but sufficing to render the stone dull and opaque; alternating with micaceous schist. At Balahulish.
- Granular quartz, of a dull aspect, in the same situation, and from the same place, with atoms of mica dispersed here and there throughout it.
- Granular quartz disposed in parallel stripes, alternately white and brown, but containing no foreign substance. From Balahulish, and in the same situation.
- The same with pyrites, and in the same situation.
- Granular quartz, deeply stained by iron, from Assynt, of various colours, yellow, red, and brown, but the grains of quartz transparent; reposing on gneiss.
- Granular quartz of a pale blue colour, containing pyrites; alternating with talc slate. Near Inverara.
- Granular rock, formed of large grains of quartz of various dark colours, and generally transparent. It contains here and there rounded and distinct grains of red opaque quartz, and of glassy felspar. From Jura.
- Dark-gray rock, of a granular splintery fracture, with pyrites. From the same place.
- Dark greenish-gray, of a similar aspect, without pyrites, extremely compact. From Sky; following mica slate.
- The same, of a darker colour, and from the same place. The influence of the weather whitens it, detecting what the magnifying glass cannot, the existence of felspar as an ingredient, and which is probably the glassy variety, since it cannot be distinguished
Vol. II.3 p