vitreum

Vitreum is a term encountered in mineralogy and historical nomenclature to denote glassy, non-crystalline substances. Derived from Latin vitreum, meaning glassy, the word is generally used descriptively rather than as an official mineral name in contemporary classifications.

In practice, vitreum commonly refers to natural glasses such as obsidian and fulgurite. These materials share an amorphous silica-based structure and a vitreous luster. Colors range from nearly colorless to black, brown, green, or translucent. Physical properties vary with composition, but most specimens have a Mohs hardness around 5–6 and a density in the general range of 2.2–2.6 g/cm3. A defining feature is conchoidal fracture, producing sharp edges when broken.

Formation and occurrence: Natural glass forms when molten or hot silica-rich materials cool rapidly enough to prevent crystalline growth. Obsidian forms from high-silica lava, while fulgurites result from rapid cooling of sand or rock after a lightning strike. Tektites are sometimes included as a related glassy product formed by impacts. Natural glass is found in volcanic terranes, deserts, and impact or lightning-impressed sites worldwide.

Uses and significance: Historically, vitreous materials such as obsidian played a crucial role in tool-making and ornamentation. In modern contexts, these materials are valued in lapidary work, as educational specimens, and as decorative glass. Safety considerations include the sharp fracture of glass shards and potential fragility of some specimens.

See also: Glass, Obsidian, Fulgurite, Tektite.