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A number of the discs show considerable wear. When I get home tomorrow I'll look some of these out. The material is very interesting, because as far as I can see no one in China knows what it is. They just call it lin fong shi (綠松石) - ie turquoise). Some of the discs and other carvings in this material are turquoise in colour, some a darker blue, and others are greenish. This may well depend on the crystal size, which in turn would depend on the temperature it was heated to, and the subsequent rate of cooling. Also when I looked at them there seemed to be two types of micro-crystals, one that transmitted red light but not blue, and the other was white and opaque. (This was only evident at the edge of the wedge, which is one crystal thick) Presumably one calcite (calcium carbonate), and one dolomite (Calcium magnesium carbonate). The equal proportions of calcite and dolomite suggest the original rock that was heated and cooled was dolosite.