Pyrite in Depth
Iron sulfide with impossible geometry
Pyrite is iron disulfide, and its crystals are the reason people first suspected minerals grow by rule rather than by accident. It forms in the cubic system and produces near-perfect cubes with faint parallel striations on the faces, running at ninety degrees to each other on adjacent faces. It also forms pyritohedra, twelve-sided solids with pentagonal faces, and eight-sided octahedra.
The cubes from Navajún in La Rioja, Spain are so sharp that people assume they are machined. Peru produces the striking stepped and hopper-faced clusters. Pyrite runs 6 to 6.5 on Mohs, which is one of the fast ways to separate it from gold: gold is soft and malleable, pyrite is hard and brittle and shatters rather than dents.
Pyrite disease, and how to avoid it
Pyrite has a real preservation problem that collectors call pyrite decay. In humid air, particularly with reactive material, the sulfide oxidizes. The specimen sprouts white or yellowish powder, develops a rusty crust, cracks apart, and produces sulfuric acid that damages whatever it is sitting on. Museum collections lose specimens to this regularly.
The prevention is dryness. Keep pyrite out of bathrooms, never soak it, never leave it wet, and never use salt water on it. If you must clean it, a dry soft brush is right. Store it in a dry place, ideally with a silica gel packet in the drawer. A well-kept pyrite cube stays bright for decades; a neglected one can fall apart in a few damp years.
What it is used for
Fool's gold is an unfair name for a mineral that has been mined for centuries for sulfur and for its trace gold content, and that gave the world its first spark-striking fire tools. The metaphysical tradition picks up the gold association and runs it toward abundance, but the more specific and more useful framing is action and confidence rather than luck.
Practitioners keep pyrite on a desk, in a workshop, or near where work actually happens rather than tucked in a drawer. A cube on a stack of paperwork is a common and slightly literal placement. It is used at the solar plexus in layouts. None of this is financial guidance, and it works best treated as a reminder to do the thing rather than a substitute for doing it.
Pairings
Leo is the primary sign association, with Aries also common, and it belongs to the solar plexus with a secondary root link. Its themes of will and follow-through fit the fire signs comfortably.
It pairs naturally with citrine, since the two split intention and execution between them, and with tiger's eye for steadiness under pressure. Lapis lazuli already contains pyrite, so the two together look and feel coherent. Keep pyrite away from any stone you regularly rinse, since the shared water dish is exactly how good pyrite gets ruined.