Pyrites, Hematite
These two metallic minerals were employed in ancient jewellery. The former, sulphide of iron, FeS2, is brass-yellow in colour, and has a specific gravity 5·2, and hardness 6½ on Mohs’s scale. It is found, when fresh, in brilliant cubes. The latter, oxide of iron, Fe2O3, has a black metallic lustre, but, when powdered, is red in colour—a mode of distinguishing it from other minerals of similar appearance. Its specific gravity is 5·3, and hardness 6½ on Mohs’s scale. In modern times it has been cut in spherical form to imitate black pearls, but can easily be recognized by its greater density and hardness. Hematite is used for signet stones, often with an intaglio engraving.