Crystal
Fool's gold, in cubes so perfect they look machined — and named for the sparks it throws.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Iron sulfide crystallises in the cubic system, and pyrite takes that literally: the Navajún mine in Spain produces cubes with faces so flat and edges so square that first-time viewers routinely assume they have been cut. They have not. It also forms pyritohedra, and in some shales it grows as flat radiating discs known as pyrite suns.
The name is from Greek pyritēs lithos, stone of fire, because struck against steel it throws a good spark — a fire-lighting technology older than the flint-and-steel kits that replaced it, and the origin of the wheel-lock mechanism in early firearms. Fool's gold came later, and the confusion was real enough to have wrecked at least one Elizabethan expedition: Martin Frobisher shipped home more than a thousand tonnes of Arctic ore in the 1570s that turned out to be worthless.
Practice puts it with money and with will, the two often bundled together as the stone that helps you do the thing rather than merely want it. One honest caution: pyrite decays. In humid storage it oxidises, crumbles and gives off sulfuric acid, which is bad for the specimen and worse for whatever it is sitting next to. Keep it dry.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Common in contemporary practice
Kept where money is handled, in the same slot citrine occupies, but with a different justification — where citrine is treated as attracting, pyrite is treated as holding. The distinction is folk taxonomy and nothing more, but it is consistently drawn.
Carried forward
Pliny the Elder, Natural History, Book 36 (c. 77 CE)
Pliny notes that pyrites gives out sparks when struck with iron, and that there is a kind which is hot to the touch. He is bundling several minerals under one name, but the fire-striking observation is exact and is the reason the stone is called what it is.
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.