Apatite is a group of minerals belonging to the hexagonal crystal system with the chemical formula of Ca5(PO4)3(F,Cl,OH). It has a variety of colors and is usually transparent to translucent. The most common apatite is the fluorine-rich type, known as fluorapatite. Blue apatite is particularly rare and popular. Previous research indicates that due to the similarity between the optical absorption and emission spectra of natural blue apatite and synthetic compounds containing MnO43–, the blue color results from the substitution of PO43– with MnO43– (P.D. Johnson et al., “Apatite: Origin of blue color,” Science, Vol. 141, No. 3586, pp.1179–1180). Chatoyancy is a very common phenomenon in apatite crystals with green or yellow bodycolors. Deep blue apatite with a cat’s-eye effect, however, is very rare.
At this year’s GJX show in Tucson, Duarte & Bastos Ltd. from Teófilo Otoni, Brazil, exhibited a 12.50 ct intense blue cat’s-eye apatite cabochon (figure 1). The stone was said to be from Brazil. It had a neon blue bodycolor and a very sharp eye seen with a spot light source. Further research is needed to verify the color origin of this stone.