Pyrite occurs as a common, widely distributed mineral with a brassy, metallic yellow luster and often a distinctive cubic or striated crystal form, found in association with many other ores and readily mistaken, by color alone, for native gold, a confusion common enough among inexperienced prospectors and miners across history to give the mineral its enduring popular name, fool's gold. Struck sharply against steel, flint or another piece of pyrite, it throws a shower of sparks hot enough to ignite tinder, a practical property that made pyrite, alongside flint, a genuine everyday firestarting material for a very long stretch of human history, and that gave the mineral its Greek derived name, from pyr, fire.
Alchemists took a real interest in pyrite for reasons beyond its resemblance to gold: weathered pyrite, exposed to air and moisture, oxidizes naturally into a green vitriol crust, meaning pyrite deposits were themselves a natural source of the iron vitriol so heavily used across the workshop, and observing this transformation directly connected the mineral world to the vitriol chemistry alchemists practiced deliberately. Pyrite was also examined, and sometimes deliberately roasted, as a source of sulfur and of iron compounds more generally, its abundance making it a convenient raw material even where a purer or more specific mineral might have been preferred in principle.