Pyrite in depth: crystal habit, and a real conservation problem

Beyond the gold comparison, pyrite is worth knowing on its own terms. It commonly forms sharp cubic crystals, sometimes with fine parallel striations across the crystal faces, a genuinely useful identifying habit since gold almost never forms true cubic crystals. Pyrite has a hardness around 6 to 6.5 and a greenish black to black streak. A real, well documented issue in mineral collections is sometimes called pyrite disease, where certain pyrite and marcasite specimens slowly oxidize over years in storage, developing a white sulfate coating and eventually crumbling, a genuine long term conservation concern for anyone keeping pyrite specimens in a permanent collection.