Quartz

Hardness: 7 on Mohs scale. Color: Typically colorless or white, but can occur in various colors like pink (rose quartz), purple (amethyst), yellow (citrine), brown (smoky quartz), and black. Luster: Vitreous (glassy). Crystal Structure: Hexagonal (trigonal system). Cleavage: None, exhibits conchoidal fracture. Specific Gravity: 2.65.

Quartz forms in a wide range of geological environments. It can crystallize from magmatic and volcanic rocks (igneous), be deposited from hydrothermal veins, or form during metamorphism. It is also a major component of sandstones and other sedimentary rocks, as it is highly resistant to weathering. Geological age varies greatly depending on the specific formation, ranging from Precambrian to present day.

Industry: Used in glass manufacturing, abrasives, electronics (as oscillators due to piezoelectricity), optics, and as a filler in paints and plastics. Jewelry: Many varieties are popular gemstones (e.g., amethyst, citrine, rose quartz, smoky quartz). Construction: Significant component of concrete and mortar as aggregate; used in engineered stone. Collecting: Individual crystals and specimens of various forms and colors are highly sought after by collectors.

Quartz is one of the most common minerals on Earth's crust, making up about 12% of the crust's volume. It has been used by humans for tools, jewelry, and spiritual purposes for thousands of years. Varieties like amethyst and citrine are popular gemstones. Pure quartz is used in oscillators for radios, watches, and computers due to its piezoelectric properties.

In the field, quartz can be identified by its glassy luster, hardness (it can scratch glass), lack of cleavage, and conchoidal fracture. It is commonly found in igneous rocks (granite, rhyolite), metamorphic rocks (gneiss, schist), and sedimentary rocks (sandstone, quartzite). It also occurs in hydrothermal veins and pegmatites. The specimen appears to be a tumbled or polished piece of milky/white quartz. When encountering it in the field, look for its distinctive crystalline forms (hexagonal prisms with pyramidal terminations) or its characteristic fracture in massive forms.