Introduction to mineralogy. Crystallography and petrology / Введение в минералогию. Кристаллография и петрология

We are all familiar with the subdivision of the natural world into the plant, animal, and mineral kingdoms. Of these the realm of minerals is the study and research area of mineralogy. A mineralogist uses the word mineral, however, in a much more restricted sense than prevails with common usage. If we examine a rock rather closely, we notice, for example, that a sandstone is composed of individual quartz grains. When we examine a specimen of granite, we can recog-inze feldspar, dark mica, and perhaps also hornblende, in addition to quartz. From a specimen of certain ores, galena, chalcopyrite, and sphalerite all shine forth brilliantly. Any such individual rock constituent is a mineral. Mineralogy encompasses the study of these minerals and the manner in which they occur, and includes the properties of all rock materials, which, in the sense used here, embrace ore and salt deposits, as well as other useful mineral deposits.
Minerals occur as constituents of rocks not only in assemblage, but are found also as separate individuals. Frequently these have the opportunity to develop without restriction in cavities or in surrounding media which could yield to then-growth. Under these conditions they often develop into polyhedral forms called crystals. These have from time immemorial attracted the attention of thoughtful natural scientists as well as laymen. <...>