Pyrite (or Fool's Gold)

Pyrite has a Mohs hardness of 6-6.5, a metallic luster, and a brass-yellow to golden color. It forms isometric crystals, often cubes, pyritohedrons, or octahedrons, and can also be found in massive, granular, or stalactitic habits. It has an indistinct cleavage and a brittle tenacity. Its specific gravity is approximately 4.95-5.02.

Pyrite forms in a wide variety of geological environments, including hydrothermal veins, sedimentary rocks, metamorphic rocks, and as a primary mineral in igneous rocks. It can precipitate from hot, sulfur-rich fluids and is commonly associated with other sulfide minerals. Its formation is common in both oxygen-poor and oxygen-rich environments, as long as iron and sulfur are present.

Historically, pyrite was used as a source of sulfur for the production of sulfuric acid, and in some cases, as an ore of iron. Today, its primary uses are limited. It is occasionally used in low-cost jewelry, ornamental objects, and as a collector's specimen. It has also been explored for its potential in certain electronic applications due to its semiconducting properties.

Pyrite is often mistaken for gold due to its color and metallic luster, leading to its nickname 'fool's gold.' However, it is much harder than gold and will not deform easily. Pyrite can sometimes contain small amounts of gold, arsenic, or other trace elements. When exposed to air and moisture, pyrite can oxidize, forming sulfuric acid, which can contribute to acid mine drainage.

In the field, pyrite can be identified by its brassy yellow color, metallic luster, and its characteristic cubic or pyritohedral crystal forms. A key identification test is its hardness: it cannot be scratched by a copper coin and will scratch glass, unlike gold which is much softer. It also produces a greenish-black streak, while gold has a yellow streak. Pyrite is found worldwide, with notable occurrences in Spain, Peru, Italy, and the United States (e.g., Colorado, Illinois). Collectors often seek well-formed crystal specimens.