Apatite gemstone: The green blue wonder

From Wikipedia:

Apatite gemstone is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite and chlorapatite,

with high concentrations of OH⁻, F⁻ and Cl⁻ ions, respectively, in the crystal. The formula of the admixture of the four most common endmembers is written as Ca₁₀(PO₄)₆(OH,F,Cl)₂, and the crystal unit cell formulae of the individual minerals are written as Ca₁₀(PO₄)₆(OH)₂, Ca₁₀(PO₄)₆(F)₂ and Ca₁₀(PO₄)₆(Cl)₂.

The mineral was named apatite by the German geologist Abraham Gottlob Werner in 1786, although the specific mineral he had described was reclassified as fluorapatite in 1860 by the German mineralogist Karl Friedrich August Rammelsberg. Apatite is derived from the Greek απατείν (apatein), which means to deceive or to be misleading, as it was often mistaken for other minerals.^[3]

Apatite is one of a few minerals produced and used by biological micro-environmental systems. Apatite is the defining mineral for 5 on the Mohs scale. Hydroxyapatite, also known as hydroxylapatite, is the major component of tooth enamel and bone mineral. A relatively rare form of apatite in which most of the OH groups are absent and containing many carbonate and acid phosphate substitutions is a large component of bone material.

Apatite gemstone: The green blue wonder : 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 MnO₄^3–, the blue color results from the substitution of PO₄^3– with MnO₄^3– (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.