Crystal
Named for deceiving mineralogists — and the same mineral your bones and teeth are built from.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Apatite got its name because it is a fraud. The German mineralogist who described it in 1786 took the Greek apatáō, to deceive, on the grounds that the mineral had been repeatedly mistaken for beryl, tourmaline, olivine and half a dozen others depending on its colour. It sits at 5 on the Mohs scale and is one of the ten index minerals defining it.
Its real importance is agricultural: apatite is the world's principal source of phosphate, and most of the phosphorus in fertiliser began as this mineral. It is also, in the form of hydroxyapatite, the mineral component of vertebrate bone and tooth enamel — which is a genuinely arresting fact about a stone in a shop window, and one that gets used in crystal writing far past the point where it means anything. That your teeth and this stone share a formula does not imply a relationship between them.
The blue and blue-green Brazilian and Madagascan material is what most people encounter; Durango in Mexico produces yellow-green crystals in quantity. Practice associates it with appetite in the broad sense — motivation, ambition, the wish to get on with something — and its throat correspondence is common but not universal. It is soft enough that ring settings are a poor idea.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Common in contemporary practice
Kept for motivation rather than focus — the difference between wanting to begin and being able to continue. Practitioners who make this distinction usually pair it with fluorite, which they assign the other half of the job.
Carried forward
Common in contemporary practice
Frequently introduced with the fact that bone and tooth enamel are made of the same mineral family. The fact is true and the inference regularly drawn from it is not; sharing a formula with a stone implies nothing at all about what the stone does.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.