Obsidian is a naturally occurring volcanic glass formed when silica-rich lava cools so rapidly that crystals do not have time to develop. Unlike meteorites, tektites, or impactites, obsidian is entirely terrestrial in origin, created through volcanic activity rather than cosmic events. However, it shares many visual and structural similarities with impact-formed glass, making it a natural complement within collections of glassy materials. Found in volcanic regions around the world, obsidian has been valued for thousands of years for both its beauty and practical uses, from tools to adornments and sacred objects.

Obsidian is typically deep black in colour, though it can also appear in shades of brown, green, or even with iridescent sheens such as rainbow or gold sheen varieties. It often forms with a smooth, glassy surface and exhibits a characteristic conchoidal fracture, producing extremely sharp edges. Variations such as snowflake obsidian, which contains white crystal patterns, and obsidian bombs, usually occurring as smaller rounded individual masses, highlight the subtle differences in formation, cooling, and composition. Its uniform texture and natural lustre make it highly desirable for display, carving, and jewelry.

Studying obsidian provides insight into volcanic processes, rapid cooling of molten material, and the formation of natural glass on Earth. It serves as a useful comparison to impact glasses, helping to distinguish between volcanic and impact-related origins. For collectors, obsidian offers an accessible and visually striking addition to meteorite and tektite collections, broadening the story of natural glass formation. Each piece represents the dynamic forces within Earth itself, complementing the extraterrestrial materials formed beyond our planet.