gems, Fischer-Book, quartz

Although quartz is abundantly distributed across the Earth and is widely known in all directions, there are still finer aspects that have not been sufficiently considered until now. I have elaborated on the mineralogically important details of this subject in my Critically Microscopic Mineralogical Studies, II. continuation, Freiburg 1873. Here, I would like to discuss some aspects from an archaeological standpoint, which may hold significant importance. The purest form of quartz, known as rock crystal or Bergkristall, is completely colorless and transparent. What is particularly important for our present discussion is that its fracture surface is generally small and rough, somewhat uneven under magnification, and is typically marked by fine, elevated, parallel curved streaks. However, it requires some caution when identifying a surface of rock crystal, as planes that do not appear as smooth crystal faces are often made up of a series of imperfectly formed individuals closely aligned side by side. The true fracture surfaces of rock crystal are more or less glassy, somewhat resembling glass. A thin shard, when examined under a polarizing microscope, shows a uniform color pattern, indicating the uniform polarization of a single mineralogical individual. With the exception of its colorlessness, the same general characteristics apply to the colored varieties of the noble quartz, which have been given names like smoky quartz, citrine, and amethyst, as well as to milk quartz, which are colored through inorganic or organic pigments.