ON QUARTZ * 

 By H. R. Moisbr, F.G.S. 

 (ABSTRACT.) 



Quartz is the most abundant of all minerals. Considered as to its 

 chemical composition, it consists chiefly of silica with a slight 

 admixture of various other substances, which impart to it the different 

 shades of colour. In a pure state it is distinguished by the formula 

 Si Og and is known under two modifications, one of which is insoluble 

 in water and all known acids excepting the hydrofluoric, and the 

 other soluble in water at high temperatures, especially in presence of 

 acids and alkalies. The insoluble variety of quartz may in process of 

 time become converted into the soluble variety under the influence of 

 infiltrated moisture. The soluble variety is found in nature in the 

 water of many springs, especially those which are hydrothermal, as 

 the Geysers of Iceland, also in rivers and the sea. Quartz crystal- 

 lises in the hexagonal system, and occurs most commonly in the form 

 of six-sided prisms terminated by pyramids, or in the form of single 

 or double pyramids. The faces of the prisms are frequently trans- 

 versely striated, while the faces of the pyramids are commonly plain 

 and smooth. The cleavage is very imperfect, i. e., it exhibits no 

 tendency to split in any one direction in preference to any other, and 

 breaks with a conchoidal fracture and vitreous or resinous lustre. 

 In its purest form it occurs as rock crystal, otherwise called Bristol, 

 Buxton, or Irish diamond, which is clear, transparent, and colorless ; 

 frequently, however, it is variously colored by foreign substances 

 either mechanically or chemically combined, in the former case more 

 or less opaque, in the latter commonly transparent. Rock crystal 

 occurs either (1) in crystals or crystalline grains, or (2) as a con- 

 stituent of crystalline or sedimentary rocks. In the sedimentary 

 strata the rolled massive quartz is the most abundant, where it forms 

 flint nodules, sandstones, puddingstones, conglomerates, grits and 

 sands. 



Brown or smoky quartz owes its colour to the presence of 

 carbon and nitrogen. Rose quartz is a massive rose-coloured variety 

 inclining to violet blue, and occurs at Ben Macdhui, in Scotland, and 

 at Rabenstein, in Bavaria, whence it has obtained the name of 



N. S., Vol. i.~June, 1876. 



Bead at York and District Field Kat. Soc, April, 1876. 



