Many people are surprised to learn that apatite is not an individual gemstone, but rather is the name given to a phosphate mineral group that's composed of calcium, phosphate and oxygen (along with various other elements).  The three common types of apatite are:

• Fluorapatite: The fluorine-dominant variety of apatite and the one you''ll generally find most often cut as a gemstone. It's the most common form of apatite and is usually found in igneous rocks. 

• Chlorapatite: A variety of apatite in which chlorine is more dominant. It's less common than fluorapatite and often found in metamorphic rocks.

• Hydroxylapatite: Not as common as fluorapatite, this variety of apatite contains hydroxyl ions in its chemical composition instead of fluorine or chlorine.

• In the jewellery world, we generally refer to all types of apatite as simply 'apatite', unless it's a very rare member of the apatite group that has been faceted into a gemstone (such as mimetite).

To form, apatite needs calcium and phosphate to be present. One of the most important locations for the mineral to be found is in sedimentary rocks which were created by the ancient accumulation and compression of organic matter such as bones, shells and teeth (which are all naturally rich in calcium/ phosphate). Apatite is also commonly found in igneous rocks like pegmatites, and in metamorphic rocks.

As it contain traces of a variety of elements and has thermodynamic properties, apatite is used by geologists as an important tool for exploring complex geological processes, such as the type and age of geological events. Observing how apatite behaves under different temperature and pressure conditions can be helpful for predicting and interpreting the Earth's behaviour, such as formation, stability, and transformations in various geological environments. 

Apatite comes in a range of stunning colours, including green, blue, yellow, and purple, its colouration caused by presence of different trace elements such as manganese and iron. The reason it's probably not so well known in the jewellery world is probably down to the fact that it's a soft gemstone (5 on the MOHs scale) and also prone to brittleness (I've occasionally had apatite crystals literally crumble in my hand whilst cutting them into gemstones) so most jeweller's recommend that it's suitable for special occasion wear only.

Apatite is primarily valued for its beautiful ornamental, decorative and also important scientific properties rather than any deep cultural or mythological significance. Having said that, it's interesting to see that it's increasingly being used as a gemstone to represent the spring equinox (perhaps because of its vivid blue and uplifting yellow colours), and there are more people choosing to wear neon-blue apatite as an alternative birthstone for December. 

Some fun facts about apatite: In ancient times powdered apatite was used as a pigment, and traces of it have been found in the famous Terracotta Army of 3rd-century BC China.  Some varieties of apatite exhibit fluorescence under ultraviolet light, and moon rocks brought back by astronauts during the Apollo missions contained traces of apatite, providing valuable insights into lunar geology. A type of apatite called hydroxyapatite, is present in the human body and is a key component of our bones and teeth!