The Mogok Stone Tract in Myanmar (formerly Burma) is one of the world’s most famous sources of ruby, which often forms there in a calcite-marble host. Calcite may occur as an inclusion inside the ruby, as in the example above. In this stone, the calcite is easy to spot between crossed polarizers, which reveal polysynthetic twinning planes that “crisscross” the crystal. While calcite is a common inclusion in ruby, this is the clearest example of calcite twinning this author has seen. Surrounding the calcite crystal is a dense, angular nest of exsolved rutile silk as short needles, a typical scene in rubies from this locality.
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