Crystal
Green quartz shot through with mica — and named, backwards, after a glass made by accident in Murano.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
The name comes from glass, not from stone. Sometime in the seventeenth century a Murano glasshouse spilled copper filings into a molten batch and produced a glittering material they called avventurina, from a ventura — by chance. When mineralogists later met a natural quartz with the same sparkle they named it after the imitation, which makes aventurine one of the few stones whose name runs the wrong way round.
The sparkle is inclusions of mica: green from fuchsite, a chromium-bearing muscovite, which is why the commonest colour is green; other varieties are coloured by hematite or goethite and run peach, red or grey-blue. Most commercial material is a quartzite rather than single-crystal quartz, and India has been the dominant source for over a century.
It occupies an odd place in practice — assigned to luck and to opportunity, and specifically to the sort of luck you have to be positioned for rather than the kind that falls on you. The word chance sitting in its name is presumably not a coincidence in the development of that reading, though nobody seems to have written the connection down.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Common in contemporary practice
Carried into interviews, auditions and anything else where the outcome is partly out of your hands. The distinction practitioners draw is between luck and readiness for luck, which is a more defensible thing to keep a stone for than most.
Carried forward
Common in contemporary practice
Regularly sold as Indian jade, which it is not. The material is genuine aventurine and perfectly good; the name is a trade fiction that has been in circulation long enough to look official.
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.