Ore microscopy and ore petrography / Минераграфия и петрография полезных ископаемых

The ore microscope is the basic instrument for the petrographic examination of the large and economically important group of minerals referred to collectively as "ore" or "opaque" minerals. Although neither term is strictly correct (inasmuch as pyrite is opaque but rarely, if ever, constitutes an economically viable ore and sphalerite and cassiterite are important ore minerals but are not opaque), both terms are frequently used synonymously. The ore microscope is similar to conventional petrographic microscopes in the systems of lense s, polarizer, analyzer, and various diaphragms employed, but differs in that its primary method of illumination is a light source above the sample to allow examination by light reflected from polished surfaces. The increasing interest in ore-gangue relationships and the recognition that much textural information can be derived from the examination of translucent ore minerals in polished thin sections now commonly leads to the use of microscop es equipped for both reflected- and transmitted-light study. The discu ssion below is concerned specifically with the design and use of the standard components of the reflected-light microscope; further details of the transmittedlight and reflected-light microscopes are described by Cameron (1961),Bloss (1961), Galopin and Henry (1972), Piller (1977), Bowie and Simpson (1977), and Criddle (1990). <...>