Apatite is the mineral your skeleton is made of. It is the actual material of bone. Bone and tooth enamel are calcium phosphate in the apatite family, and the same mineral turns up in rock all over the world in a range of colours.

Apatite comes from the Greek apate, meaning deceit, and it was given in 1786 because the mineral kept being mistaken for other things: beryl, tourmaline, olivine, topaz. It has been confusing people for centuries and it still does, because apatite is one of the few minerals that comes in more colours than almost anything else: blue, green, yellow, pink, purple, brown, colourless, and in the same deposit as one another. 

Blue is the material most often seen on the market, and it is the colour that has made the stone's name in modern crystal retail.

The blue is genuinely blue in the natural material, and it is not a subtle shade. Good crystals are a clear, almost electric blue with a green edge in certain lights, and they are usually small. On the hardness scale apatite sits at five. That is the same as a steel knife blade. It is hard enough to polish, soft enough to scratch with a blade, and soft enough that it will wear if it is kept in a pocket with anything harder. It also means it can be carved and faceted, and it is a favourite of gem cutters for that reason.

Deposits of the blue material come out of Madagascar, Brazil, Myanmar and Mexico. Because the colour is uneven, one face of a piece is often a brighter blue than the rest, and the stone commonly carries small patches of iron staining that read as rust or orange across the surface.

Traditionally associated with

Apatite has no old folk tradition. It was a mineral before it was a crystal in the shop sense, and its history is that of a scientific curiosity. 

In modern practice it is kept as a display piece and grouped with the blue stones, and it is most often set on a shelf or a desk.

How I'd keep it

Five on the hardness scale means care rather than caution. Wash it in cool water with a soft cloth and dry it properly, and keep it away from acids, bleach and household cleaners. Never scrub it and never use an abrasive pad, because anything harder than the stone will take the surface off. Do not store a rough piece loose in a drawer with quartz, agate or anything else above five, as the piece will be the one that comes off worse. It is stable in light and does not fade.

What to watch for

The confusion the stone is named for is still the main thing to check. Blue apatite is regularly sold as aquamarine, and the two look close in a photograph. 

Aquamarine is a beryl and sits at seven and a half, so the test is simple: if a piece is being sold as aquamarine and is soft enough to mark, it is not aquamarine. 

Dyed material is also common with the yellow and green material, and the tell is the usual one. Colour pooling in the cracks rather than running through the stone. 

Blue apatite with genuine colour needs no treatment, so be wary of a seller describing treatment at all.

In the shop

Rough Apatite is available from £10, and each piece is a one-off, so the stone in the photograph is the one that arrives.

Free UK shipping on orders over £50. Everything is sent from Luton, and collection is available if you're local.