Mohs hardness scale, and where every birthstone sits
The Mohs scale ranks minerals from 1 (talc) to 10 (diamond) by which can scratch which. It is a ranking, not a measurement: the steps are uneven, and diamond is many times harder than corundum (ruby and sapphire) even though it is only one step higher.
The 10 reference minerals
- 1 Talc
- 2 Gypsum
- 3 Calcite
- 4 Fluorite
- 5 Apatite
- 6 Orthoclase feldspar
- 7 Quartz
- 8 Topaz
- 9 Corundum
- 10 Diamond
Reference minerals: Eastern Illinois University: Mohs hardness scale.
Birthstone hardness chart
Hardness for each gem from its GIA care guide (diamond: Mohs reference mineral 10). Bloodstone is left out because our sources do not give a figure.
Hardness is not the whole story
Hardness is resistance to scratching. Toughness is resistance to chipping and breaking, and the two do not always go together. Topaz rates 8 but GIA rates its toughness poor because of its cleavage, so a hard knock can split it. Ruby and sapphire (9) combine hardness with excellent toughness. That is why we rate everyday wear separately: see the everyday wear checker.
Why it matters for cleaning and storage
Household dust contains quartz (7), so any gem softer than 7 slowly gets scratched by ordinary dust and by harder gems in the same box. Store soft stones such as opal, turquoise and pearl separately.
Frequently asked questions
What is the hardest birthstone?
Diamond (April) at 10. Ruby and sapphire are 9, alexandrite 8.5, and topaz and spinel 8.
What is the softest birthstone?
Pearl, at 2.5 according to GIA. Turquoise (5 to 6) and opal (5 to 6.5) are also soft.
Can a diamond be scratched?
Only by another diamond, according to the American Gem Society. It can still chip if struck at the wrong angle.