Smoky Quartz

Hardness: 7 on Mohs scale. Color: Translucent to opaque brown, grayish-brown, or black. Luster: Vitreous (glassy). Crystal Structure: Hexagonal (trigonal crystal system). Cleavage: None, exhibits conchoidal fracture. Specific Gravity: 2.65.

Smoky Quartz forms in igneous rocks like granite and pegmatite, as well as in metamorphic and some sedimentary rocks, typically in hydrothermal veins. Its brownish color is believed to be caused by natural irradiation of aluminum impurities within the crystal structure. This irradiation alters the valence states of some atoms, leading to color centers. Geological age varies widely, often forming with the host rock, which can range from millions to billions of years old.

It is widely used in jewelry as a gemstone (often faceted or carved into beads like those pictured). Due to its piezoelectric properties, quartz in general is used in oscillators, clocks, and radio transmitters, though clear quartz is preferred for these applications. Larger specimens can be used for ornamental pieces and carvings.

Smoky quartz is a variety of quartz, which is the second most abundant mineral in the Earth's continental crust. Its color can sometimes be artificially induced by exposing clear quartz to radiation. Historically, it has been used for various purposes, including sunglasses in ancient China and for crystal balls. Morion is a very dark, opaque variety of smoky quartz.

In the field, smoky quartz can be identified by its characteristic smoky brown color, vitreous luster, hardness (it can scratch glass), and hexagonal crystal form (when found as euhedral crystals). It's commonly found in mountainous regions globally, with significant deposits in Brazil, Madagascar, the Swiss Alps, and the United States (e.g., Colorado, New England). Tips for collectors include looking in pegmatites, hydrothermal veins, and fractured zones within granitic rocks. Its often-striated crystal faces and conchoidal fracture are good identifiers. The beads in the image are polished and drilled, indicating they have been processed for jewelry.