GeoMiner Free earth-science tools

Built by a geologist

Minerals That Scratch Glass: Hardness Guide

Typical window glass is about 5.5 on the Mohs hardness scale. A mineral that produces a permanent groove may be harder than the glass, but the test is approximate and the glass composition, weathered surfaces, and technique all matter. Use a sharp, fresh mineral edge and an expendable piece of known glass—not a phone screen, lens, or vehicle window. Press firmly enough for contact, then wipe the glass clean. A removable powder line is not a scratch. Repeat on a second spot and test whether the glass can scratch the mineral for a reciprocal comparison. Combine hardness with cleavage, lustre, crystal habit, streak, and geologic setting. Quartz grains stuck to a softer specimen can scratch glass and create a false result. Weathered rinds may be softer than the fresh interior. Hardness is resistance to scratching, not resistance to breaking; a hard mineral can still be brittle.

Verification resources

Cross-check terminology, classification, methods, and safety with these authoritative external resources.

  • IMA–CNMNC List of Mineral Names — International Mineralogical Association. Official mineral-name, nomenclature, and classification records.
  • Mineral ID Key — Mineralogical Society of America. Physical-property identification methods, repeat-testing guidance, and limitations.

Read GeoMiner's editorial methodology.

JavaScript is loading the interactive GeoMiner experience. The identification tools provide educational candidates, not laboratory confirmation.