Physical Properties: Hardness & Luster

The first step in mineral identification is observing physical properties. Hardness and luster are two of the most useful and easily determined properties. Mohs Hardness Scale In 1812, Friedrich Mohs developed a relative hardness scale using 10 common minerals: | Hardness | Mineral | Common Test | |----------|---------|-------------| | 1 | Talc | Scratched by fingernail | | 2 | Gypsum | Scratched by fingernail | | 2.5 | - | Fingernail hardness | | 3 | Calcite | Scratched by copper coin | | 4 | Fluorite | Scratched by knife blade | | 5 | Apatite | Scratched by knife blade | | 5.5 | - | Knife blade/glass hardness | | 6 | Orthoclase | Scratches glass | | 7 | Quartz | Scratches steel file | | 8 | Topaz | - | | 9 | Corundum | - | | 10 | Diamond | Hardest natural substance | Testing Hardness 1. Find a fresh, unweathered surface 2. Hold the specimen firmly 3. Try to scratch it with your test materials 4. Confirm by checking for powder scratch vs. streak transferred material Luster Luster describes how light reflects from a mineral surface. There are two main categories: Metallic Luster - Looks like polished metal - Examples: Pyrite, galena, gold, silver Non-Metallic Luster Types - Vitreous glassy : Quartz, olivine - Resinous : Sphalerite, sulfur - Waxy : Serpentine, chalcedony - Pearly : Talc, muscovite - Silky : Satin spar gypsum, chrysotile - Adamantine : Diamond, zircon - Earthy/Dull : Kaolinite, limonite Pro Tip : Always examine luster on a fresh surface - weathering can dramatically change a mineral's appearance!

All lessons in Mineral ID Basics — Return to the complete Mineral ID Basics course outline.
Previous lesson: Introduction to Mineralogy — Mineralogy is the scientific study of minerals - naturally occurring, inorganic solids with a definite chemical composition and crystalline structure.
Next lesson: Physical Properties: Streak, Cleavage & Fracture — Continuing our exploration of physical properties, streak, cleavage, and fracture provide crucial diagnostic information.

Verification resources

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

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

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Physical Properties: Hardness & Luster

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Verification resources