A plain-language definition for anyone researching mohs hardness, what it is, where it comes from, and how practitioners use it.
85 plain-language definitions · Cited sources · Persona-authored
By Crystal Cassandra · Updated August 3, 2026
Crystal Healing Expert
What is mohs hardness?
Mohs hardness is a 1-10 scale that ranks minerals by their resistance to scratching. In gemology and crystal care, it determines whether a stone can safely be cleansed in water, salt, or sunlight, softer stones (below 5) often cannot.
The Mohs scale was developed by German mineralogist Friedrich Mohs in 1822. It ranks ten reference minerals from talc (1) to diamond (10), with each higher mineral able to scratch the ones below it. Most crystals used in healing fall between 2.5 (Selenite) and 8 (Topaz), though quartz family stones (Clear Quartz, Amethyst, Citrine, Rose Quartz) all sit at exactly 7.
In my practice, Mohs hardness is the single most useful technical fact for keeping a collection safe. Hold a Selenite wand (hardness 2) next to a Tourmaline (hardness 7-7.5), the Tourmaline will scratch the Selenite if they bump in storage. Stones below hardness 5 should never be cleansed in water or salt, as they can dissolve, pit, or release toxic compounds.
Friedrich Mohs introduced the scale in his 1822 textbook Grund-Riß der Mineralogie. It remains the standard gemological reference scale 200 years later, used by geologists, jewelers, and crystal healing practitioners alike. The scale is logarithmic in absolute hardness despite using simple integers, diamond is about four times harder than corundum (9), not 10% harder.
To check whether a stone can safely be cleansed in water, look up its Mohs hardness. Stones at 5.5 or above (Quartz, Tourmaline, Amethyst, Carnelian) tolerate brief water cleansing. Stones below 5 (Selenite at 2, Calcite at 3, Halite at 2-2.5) must be cleansed by alternative methods, moonlight, sound, smoke, or dry salt.
For storage, separate soft stones from hard ones. A fabric-lined drawer, a cleansing routine that respects hardness, and an awareness of which stones need extra care will preserve a collection for decades. In my practice I always note the hardness on the storage label so I never have to look it up twice.
These glossary terms are closely connected to mohs hardness:
Diamond (10) is the hardest, followed by Sapphire and Ruby (both Corundum, 9), then Topaz (8) and Spinel (7.5-8). For everyday healing work, Quartz family stones at 7 are durable and common.
Selenite, Halite, Calcite, Lapis Lazuli, Malachite, Pyrite, Hematite, and Angelite, most of which are below Mohs 5 or contain water-soluble or toxic components.
Quartz sits at hardness 7, harder than human fingernails (2.5), glass (5.5), and many softer collected minerals. If a stone scratches glass, it's likely Quartz or harder.
No. Hardness measures scratch resistance; toughness measures impact resistance. Diamond is hard but brittle and can chip on a hard impact. Nephrite Jade is much softer (6-7) but extremely tough.
Share Your Result
Vertical 9:16 format, perfect for Instagram Stories or TikTok. Opens in a new tab; long-press or right-click to save.
Free: how to choose a stone when everything looks appealing, the care matrix that tells you what is safe in water and what is not, and a first intention practice you can actually keep.
We respect your inbox. Unsubscribe anytime.