Pyrite on Calcite

Pyrite on Calcite from the Zinc Corp Mine, Broken Hill, New South Wales, Australia, measuring 125 × 55 × 40 mm and weighing 243 grams. It is a long, generous piece from one of the great twentieth-century mines on the Broken Hill line of lode.

Pyrite is iron disulfide, FeS2, the familiar brassy "fool's gold", which most often grows as cubes, pyritohedra or octahedra. Calcite is calcium carbonate, and in a combination like this the Pyrite has grown on Calcite that was already there. The primary Broken Hill ore is dominated by Galena and Sphalerite, with iron sulfides present in smaller amounts, and crystallised Pyrite and Calcite of this kind generally come from open spaces in the lode where later fluids had room to deposit crystals.

The Zinc Corporation was formed in 1905 to treat the zinc-rich tailings and ore that early Broken Hill smelting had left behind, and its mine went on to become one of the major producers on the field. Broken Hill is better known for its oxidised-zone rarities, but the primary sulfide ore is just as much part of the deposit's story, and this Zinc Corp piece from the Allan Waldon Collection represents that side of it.