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Special Diagnostic Tests

Beyond the basic physical properties, special tests can help identify minerals that might otherwise be confusing. Chemical Tests Acid Test HCl The most common field chemical test uses dilute hydrochloric acid 10% HCl : - Calcite : Effervesces vigorously fizzes in cold, dilute HCl - Dolomite : Only reacts when powdered or with warm acid - Aragonite : Reacts like calcite same composition, different structure Safety : Always wear safety glasses and handle acids with care! Taste Test Only for minerals you know are safe: - Halite : Salty taste NaCl - Sylvite : Bitter, salty taste KCl Magnetic Properties Magnetism - Magnetite : Strongly magnetic - attracts a magnet - Pyrrhotite : Weakly magnetic - Use a small magnet or compass to test Density & Heft Specific gravity SG is the ratio of a mineral's weight to an equal volume of water: - Light SG < 2.5 : Sulfur, graphite - Average SG 2.5-4 : Most silicates, carbonates - Heavy SG 4-8 : Barite, galena, many ore minerals - Very heavy SG 8 : Native gold, silver, platinum Field test : Compare "heft" - how heavy the sample feels compared to similarly-sized rocks. Optical Properties Double Refraction - Calcite : Clear calcite shows double refraction - text appears doubled when viewed through the crystal Fluorescence Under ultraviolet UV light, some minerals glow: - Fluorite : Often blue, purple, or green - Scheelite : Blue-white important for tungsten prospecting - Willemite : Green Other Properties - Piezoelectricity : Quartz generates electric charge under pressure - Odor : Sulfur smells like rotten eggs when scratched; kaolinite has an earthy smell when moistened

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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