Built by a geologist

Quartz vs Glass: Hardness, Bubbles and Crystal Clues

Clear, milky, coloured, tumbled, or broken quartz can resemble bottle glass, decorative glass, slag, beads, or natural volcanic glass. Quartz is a crystalline mineral with Mohs hardness 7 and may preserve six-sided prisms or crystal faces. Glass is amorphous, varies in composition and hardness, and may preserve rounded bubbles, flow lines, mould seams, uniform colouring, or manufactured context. Both can be transparent, glassy and conchoidally fractured, so appearance alone is not enough. A well-formed six-sided crystal, quartz-style growth surfaces, and a clean persistent scratch on common glass support quartz. Rounded bubbles, mould seams, flow lines, cast shapes, or obvious manufactured context support glass. Conchoidal fracture and a glassy lustre occur in both. Do not scratch jewellery, cut stones, display specimens, or potentially valuable material; use a gemologist or laboratory when the distinction matters. Record where the object came from and whether it was cut, polished, mounted, sold, cast, tumbled, or found near buildings, roads, rail, furnaces, dumps, or beach debris. Use a hand lens on every existing surface. Look for rounded or stretched bubbles, mould seams, flow lines, tool marks, a flat manufactured base, coatings, glue, or repeated cast shapes. Look for quartz evidence: a consistent six-sided prism, pointed termination, drusy crystal growth, interlocking grains, or growth surfaces that continue through the specimen. Treat conchoidal fracture and glassy lustre as shared clues rather than a decision. Do not create a new sharp edge merely for inspection. Only on verified expendable rough, use a clean representative edge on an expendable glass plate and confirm a persistent groove after wiping away loose powder. Stop if the specimen or plate could be valuable or hazardous. For jewellery, faceted material, suspected synthetic quartz, historic glass, or any consequential identification, preserve the object and obtain non-destructive gemological or laboratory testing. Broken glass, slag, and quartz can all have razor-sharp edges. Do not run fingers along an edge, pressure-flake the object, or carry loose shards unprotected. Do not scratch, chip, heat, flame-test, acid-test, or grind jewellery, faceted stones, artifacts, display specimens, or potentially valuable material. Bubbles are supporting evidence, not proof. Some natural quartz contains f