ROCK CRYSTAL. 175 trappean rocks along the northern shore of Lake Superior, yield amethysts in great abundance ; and the rock-crystals at Quebec, give rise to unusual modi fications of form. Large crystals are also found in the quartz veins of Bruce mine and Harvey’s Hill mine of Lower Canada. 1 Varieties. Smoke quartz. This is a clouded variety, with a brownish tint becoming deep, when it is termed morion. Rose quartz. A pink variety, the colour being probably due to a slight admixture of oxide of manganese. 2 (b) Amethyst. Violet or purple colour from oxide of manganese. The finest specimens are obtained from Ceylon, India, Persia, and Siberia. (c) Chalcedony (from Chalcedon, in Asia Minor). A milk-white or wavy, translucent variety, approach ing smalt-blue, the latter being most rare and highly esteemed. The stone is an intimate mixture of crystalline and amorphous silica; or, according to Fuchs, of silica and some opal disseminated through it. 3 It generally occurs in mammillated and bo- tryoidal forms, exhibiting in cross section parallel layers of slightly varying tints and degrees of trans- 1 Logan, Geol. of Canada, p. 500. 2 Hunt, Descrip. Guide M. P. G. p. 141. 3 Poggend. Annal. xxxi. 577. Bischof concurs in this view, Chem. and Phys. Geol. (Eng. vers.) ii. 464.
