Mohs Scale of Hardness: Crystal Durability & Care Guide

The Mohs scale of hardness is the go-to tool for understanding how durable a crystal is, how to care for it and how to keep your collection from getting scratched. Created in 1812 by German mineralogist Friedrich Mohs, this simple 1 to 10 scale tells you which stones can scratch others, which need gentle handling and which can stand up to everyday wear.

TL;DR

• The Mohs scale rates hardness from 1 (softest, talc) to 10 (hardest, diamond)
• Hardness tells you about scratch resistance, everyday durability and the safest ways to clean a stone
• Soft crystals (1 to 4) need gentle care, medium crystals (5 to 6) need some care, and hard crystals (7 to 10) are durable

Key Points:

• What Is the Mohs Scale of Hardness?
• Understanding the Mohs Scale
• Mohs Scale for Common Crystals
• Hardness & Crystal Care
• Water Safety & Mohs Scale
• Protecting Your Crystals
• Conclusion

What Is the Mohs Scale of Hardness?

The Mohs scale measures scratch hardness: how well a mineral resists being scratched by another material. Friedrich Mohs chose ten common minerals and ranked them so that each one can scratch every mineral below it. The ten reference minerals are:

1. Talc
2. Gypsum (including selenite)
3. Calcite
4. Fluorite
5. Apatite (including blue apatite)
6. Orthoclase feldspar (the family of moonstone and amazonite)
7. Quartz
8. Topaz
9. Corundum (ruby and sapphire)
10. Diamond

Understanding the Mohs Scale

The scale is relative, not even. Diamond (10) is far more than twice as hard as quartz (7). The jumps get much bigger near the top. But for crystal lovers, the order is what matters: a harder stone will scratch a softer one.

You can estimate hardness with everyday objects:

• Fingernail: about 2.5 (scratches selenite)
• Copper coin: about 3.5
• Steel knife or glass: about 5.5
• Steel file: about 6.5

Hardness is not the same as toughness. A hard stone can still chip or crack if it has natural cleavage planes (like fluorite) or if it's dropped on tile.

Mohs Scale for Common Crystals

• Selenite and satin spar: 2
• Lepidolite: 2.5 to 3
• Calcite: 3
• Malachite: 3.5 to 4
• Rhodochrosite: 3.5 to 4
• Fluorite: 4
• Obsidian: 5 to 5.5
• Lapis lazuli: 5 to 5.5
• Sodalite: 5.5 to 6
• Hematite: 5.5 to 6.5
• Labradorite and moonstone: 6 to 6.5
• Pyrite: 6 to 6.5
• Agate, jasper, carnelian: 6.5 to 7
• Amethyst, rose quartz, clear quartz, citrine, smoky quartz: 7
• Black tourmaline: 7 to 7.5

Hardness & Crystal Care

Soft stones (1 to 4): selenite, calcite, malachite and fluorite scratch easily. Handle them gently, dust them with a soft dry cloth, and avoid carrying them loose in a pocket or bag with other stones.

Medium stones (5 to 6): obsidian, lapis, hematite and labradorite are fine for display and occasional carry, but they can pick up scratches from quartz and from grit. Keep jewelry made from them separate when stored.

Hard stones (7 and up): the quartz family, agates and tourmaline are great for everyday jewelry, pocket stones and tumbling. They can scratch softer stones, so don't store them in the same pouch as selenite or fluorite.

Water Safety & Mohs Scale

A common rule of thumb is that stones below 5 shouldn't be soaked, but hardness alone doesn't decide water safety. What matters most is the stone's chemistry and structure:

• Dissolve or damage in water: selenite, halite, and many soft, porous stones.
• Contain metals or can rust: pyrite, hematite and magnetite can tarnish or rust.
• Porous or fragile: malachite, turquoise, lepidolite and some raw clusters.
• Generally water-safe for a quick rinse: quartz family, agate, jasper, carnelian, tiger's eye.

For the full list, see our guide to crystals to never put in water, and our sunlight safety guide for stones that fade.

Protecting Your Crystals

• Store soft and hard stones separately, or wrap each piece in a soft cloth.
• Use padded boxes or divided trays for jewelry.
• Display spheres and eggs on a proper stand so they can't roll.
• Take off soft-stone jewelry before washing hands, showering, swimming or exercising.
• Clean with a soft cloth instead of scrubbing brushes or chemicals.

Conclusion

The Mohs scale is a simple tool that saves a lot of heartbreak. Once you know where your crystals fall, you'll know which can ride in your pocket, which belong on a shelf, and which should never meet water. For more care tips, read our complete cleansing guide, or explore our durable quartz crystals for everyday carry.

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