Mohs Hardness Scale Minerals to Know for Mineralogy

The Mohs Hardness Scale ranks minerals based on their ability to scratch one another, providing insight into their physical properties. Understanding these minerals helps us appreciate their roles in geology, industry, and everyday life.

1. Talc (1)

   • Softest mineral on the Mohs scale, rated at 1.
   • Composed mainly of magnesium, silicon, and oxygen.
   • Commonly used in talcum powder and as a lubricant.
   • Exhibits a greasy feel and can be easily scratched with a fingernail.
   • Often found in metamorphic rocks, particularly schist.

2. Gypsum (2)

   • Rated at 2 on the Mohs scale, slightly harder than talc.
   • Composed of calcium sulfate dihydrate.
   • Used in plaster, drywall, and as a soil conditioner.
   • Can be scratched with a fingernail and has a pearly luster.
   • Occurs in sedimentary environments, often as evaporite deposits.

3. Calcite (3)

   • Rated at 3 on the Mohs scale, can be scratched by a copper coin.
   • Composed of calcium carbonate, a common sedimentary mineral.
   • Exhibits double refraction, making objects viewed through it appear doubled.
   • Found in limestone and marble, important for construction and industry.
   • Reacts with dilute hydrochloric acid, producing carbon dioxide bubbles.

4. Fluorite (4)

   • Rated at 4 on the Mohs scale, can be scratched by a knife.
   • Composed of calcium fluoride, often found in hydrothermal veins.
   • Exhibits a wide range of colors and fluorescence under UV light.
   • Used in the production of aluminum, gasoline, and as a flux in steelmaking.
   • Forms cubic crystals, which are distinctive and easily recognizable.

5. Apatite (5)

   • Rated at 5 on the Mohs scale, can be scratched by a steel file.
   • Composed of calcium phosphate, a key component of bones and teeth.
   • Important for the production of fertilizers and phosphoric acid.
   • Exhibits a variety of colors and can form hexagonal crystals.
   • Found in igneous, metamorphic, and sedimentary rocks.

6. Orthoclase feldspar (6)

   • Rated at 6 on the Mohs scale, can be scratched by a glass plate.
   • Composed of potassium aluminum silicate, a major component of granite.
   • Exhibits two directions of perfect cleavage at right angles.
   • Used in ceramics, glass production, and as a filler in various products.
   • Can appear in a range of colors, including pink, white, and green.

7. Quartz (7)

   • Rated at 7 on the Mohs scale, can scratch glass and most metals.
   • Composed of silicon dioxide, one of the most abundant minerals in the Earth's crust.
   • Exhibits a wide variety of colors and forms, including amethyst and citrine.
   • Used in electronics, glassmaking, and as a gemstone.
   • Has a conchoidal fracture and is resistant to weathering.

8. Topaz (8)

   • Rated at 8 on the Mohs scale, can scratch quartz and most other minerals.
   • Composed of aluminum silicate fluoride hydroxide.
   • Often found in igneous rocks and can form large, well-formed crystals.
   • Used as a gemstone in jewelry, available in various colors.
   • Exhibits perfect cleavage in one direction, making it prone to splitting.

9. Corundum (9)

   • Rated at 9 on the Mohs scale, second hardest mineral after diamond.
   • Composed of aluminum oxide, found in metamorphic rocks.
   • Forms rubies and sapphires, highly valued as gemstones.
   • Used as an abrasive in industrial applications due to its hardness.
   • Exhibits a hexagonal crystal system and has no cleavage.

10. Diamond (10)

    • Hardest known natural material, rated at 10 on the Mohs scale.
    • Composed of carbon atoms arranged in a crystal lattice structure.
    • Highly valued as gemstones and for industrial cutting tools.
    • Exhibits exceptional brilliance and fire due to its high refractive index.
    • Forms under high-pressure, high-temperature conditions deep within the Earth.