Rare Blue Apatite Inclusion in Smoky Quartz
A natural smoky quartz with an obvious mineral inclusion at the center of the stone (figure 1) was recently observed by the author. Raman analysis confirmed that this mineral was apatite. The apatite had very light blue color and a hexagonal twinned morphology. Under cross-polarized light, the inclusion showed interference colors, confirming its doubly refractive nature (figure 2).
Apatite is a phosphate mineral with the chemical formula of Ca5(PO4)3(Cl/F/OH). Generally, smoky quartz and apatite can occur under the same geologic conditions, including pegmatitic hydrothermal environments. Apatite is commonly a protogenetic inclusion, but it can occasionally result from a later stage and be considered a syngenetic inclusion in quartz. The rounded shape of this apatite example suggests a protogenetic inclusion, one that would be a welcome sight for any gemologist examining stones in a microscope.
