Quartz and Pyrite

Quartz

Quartz is one of the most widespread minerals and the one with the most varieties. These are divided into two main groups, depending on whether they are minerals with clearly visible crystals or minerals formed by aggregates of microscopic crystals. The first group includes pure quartz (hyaline quartz or rock crystal), colourless and transparent, amethyst quartz, smoky quartz or morion, citrine quartz, blue quartz, iris quartz and rose quartz, varieties coloured by impurities. The second group, on the other hand, includes chalcedony (which in turn comprises carnelian, agate and onyx), jasper and flint.

It forms hexagonal prisms, it is stubby or slender, with pyramidal terminations. Quartz is a hard mineral, light, it is not fusible, it is insoluble, except in hydrofluoric acid.

It forms in igneous rocks, metamorphic and sedimentary, and is also frequent in veins of metallic minerals.

Quartz is used in many sectors: domestic (detergents and toothpastes), industrial (glassworks), gemmological for the finest specimens, and also technological (oscillators, ultrasound generators).

Pyrite

Pyrite, a very well-known and widespread mineral, forms cubic crystals, with smooth or striated faces, octahedral, pentagonal dodecahedral. It sometimes also occurs in compact masses, granular, stalactitic and nodular. This mineral is hard, brittle, heavy and opaque.

If struck with a metal object it produces sparks. It melts easily, releasing a strong smell of zinc and, if placed in humid environments it turns into sulphuric acid and other products.

The fact that pyrite is so frequent is due to its forming in various geological environments: in hydrothermal veins, in metamorphic rocks, magmatic and sedimentary rocks.

Pyrite is used for the extraction of gold and nickel and for the production of sulphuric acid, copper, iron and steel.