XXVII. Quartz as a Rock-forming Mineral

Abstract

In the few remarks which I have to bring before the Society this evening, I make no pretensions of offering any original observations on the mineral Quartz. What I have to state, for the information of the younger members, is only what has been made known during recent years in Geological Text-Books and in special papers, as to its modes of occurrence, the conditions under which it is found, and the important place it occupies, as one of the rock-forming minerals, it being estimated to form one fourth, perhaps, of the ponderable crust of the globe. Quartz, a German miner's term for crystallized silica or rock crystal, is a mineral which is properly speaking colourless, but found of all tints when mixed with various metallic elements which are considered impurities, although sometimes they give it great beauty and interest, especially in those varieties known as gem-stones. In the scale of hardness of minerals, ranging from 1 to 10, quartz reaches 7, so that there are only 3 degrees between it and the diamond, which has a hardness of 10. Quartz is an oxide of silicon, there being in 100 parts 53·33 of oxygen, and 46·67 of silicon, or silicium as it is sometimes termed, a dark brown powder, heavier than water, which, the base of silica, was first discovered by Berzelius in 1823, and is still only known to the scientific chemist. It is non-fusible before the blow-pipe and non-volatile. Silica or quartz possesses one or two interesting and valuable This 250-word extract was created in the absence of an abstract