Apatite is a family of minerals which are mostly mined for commercial and industrial purposes. Apatite is a 5 on the mohs scale of hardness and is a phosphate mineral. 

Phosphates are very important for plant life and apatite is a main source in soil. 

Most "apatite" is fluorapatite, whereas hydroxylapatite is much less common and chlorapatite is very rare. Most apatites are green but most of the gem apatite we encounter is blue. 

Apatite is soft for an every day wear ring but can have phenomenal color!