Volcanic glass and visual varieties
Snowflake, mahogany and sheen names describe volcanic glass appearances; they are not independent mineral species.
Keep each chapter’s scientific identity: a family, species, variety, trade label, rock and fossil are different kinds of names.
Natural glass
Obsidian is natural volcanic glass, commonly dark and strongly reflective. It offers a useful contrast to crystalline minerals: its geological story is one of rapid cooling rather than a large, ordered crystal growing into space.
Dexter Perkins · CC0 · Display crop
Natural glass variety
Snowflake obsidian has gray-white rounded crystalline patches in dark volcanic glass. The contrast can make a small polished piece easy to study.
Mike Davis · CC0 1.0 · Display crop
Natural glass variety
Mahogany obsidian is a trade variety of volcanic glass with reddish-brown and black patterning. Its polish reveals broad color areas rather than individual pointed crystals.
Mariana J. Espinoza · CC BY-SA 4.0 · Display crop
Optical variety of volcanic glass
Gold-like sheen is an optical effect in volcanic glass, not proof of gold content. The flash depends on viewing geometry; inspect the surface for coatings and ask about treatment.
United States Forest Service · Public domain · Display crop
Optical variety of volcanic glass
A silvery reflection gives the trade name. It is not a silver-bearing mineral species, and a metallic-looking surface does not establish untreated natural sheen.
James St. John · CC BY 2.0 · Display crop
Optical variety of volcanic glass
Colored iridescent bands vary with light and orientation. The material remains volcanic glass; internal structures and possible surface treatments need to be distinguished.
Brocken Inaglory · CC BY-SA 3.0 · Display crop