A mineral is a naturally occuring, homogeneous, solid with a crystalline atomic structure. Crystallinity implies that a mineral has a definite and limited range of composition, and that the composition is expressible as a chemical formula. Some definitions of minerals give them as inorganic materials, however both diamonds and graphite are considered minerals, and both are primarily comprised of carbon, which would make them organic. So this leads me, as an engineer, to believe that mineralogists do not have a good, precise definition of a mineral, but rather a loose definition. The definition above, is the most inclusive and would include all substances currently described as minerals. The key items that make something a mineral are occurring naturally, and the definite crystal structure, that is expressible as a chemical formula. Rocks that do not meet this criteria are referred to as amorphis - not having a definite structure or expressible as a chemical formula. Some elements that occur naturally and are minerals are arsenic, bismuth, platinum, gold, silver, copper, and sulphur.

THE DEFINITION OF ORGANIC: Organic chemistry is the study of those substances containing carbon in combination with hydrogen (H), and a few other non metals, namely oxygen (O), nitrogen (N), sulfur (S) and the halogens (F2, Cl2, Br2, and I2).

This specemin is from the Huanzala Mine in Central Peru

Pyrite is commonly called "fools gold", is cubic, frequently found in many distorted shapes. It has a hardness of 6 to 6.5, a specific gravity of 4.9 to 5.2, has a brassy color, is sometimes tarnished with brown, and has a greenish to black streak. Pyrite decomposes readily in a wet environment, and limonite and goethite are usual decompositions of pyrite. It is the most common sulphide mineral ond is widely distributed on earth. Pyrite is a source of sulphur and can be used to manufacture sulpheric acid and iron sulphate.