Gemstone hardness chart: what is the hardest gem after diamond?

Quick answerUpdated October 17, 2026

The hardest gem after diamond (10 on the scale) is moissanite, a lab-made gem at 9.25; the hardest natural gems after diamond are ruby and sapphire, both at 9. Next come alexandrite at 8.5, then spinel and topaz at 8. GIA calls gems of 8 or above ideal for everyday wear, such as engagement rings.

What is the hardest gemstone after diamond?

Moissanite, if you count lab-made gems; ruby and sapphire, if you count only natural ones. Diamond is 10 on the Mohs scale, and GIA puts moissanite (; all moissanite used in jewellery today is lab-created) at 9.25, second only to diamond. Ruby and sapphire are both corundum, at 9. Below them comes alexandrite, the colour-change variety of chrysoberyl, at 8.5, then spinel and topaz at 8. The gap at the top is bigger than the numbers suggest: GIA points out that the scale is not incremental, and that diamond is about four times harder than sapphire, although they are only one step apart.

Gemstone hardness chart: where does each gem sit on the Mohs scale?

A harder gem scratches a softer one, and only a diamond can scratch a diamond. Values are from GIA and the Handbook of Mineralogy (hosted by the Mineralogical Society of America); a range means the figure varies between specimens, species or types. A lab-grown gem sold under a natural gem’s name has essentially the same physical properties as that gem, so the same hardness.

Gem	Mineral	Mohs hardness	Everyday ring?	Good to know
Diamond, mined or lab-grown	Carbon	10	Yes	Hardest gem, but it has cleavage directions: GIA warns a hard blow can still cleave it
Moissanite	Silicon carbide, lab-made	9.25	Yes	Second only to diamond; GIA found no prominent cleavage
Ruby and sapphire	Corundum	9	Yes	The hardest natural gems after diamond
Alexandrite	Chrysoberyl	8.5	Yes	GIA: good durability for everyday wear
Cubic zirconia (CZ)	Zirconium dioxide, lab-made; a diamond simulant	8 to 8.5	Yes, but it scratches over time	Softer than moissanite and sapphire
Spinel	Spinel	8	Yes	GIA: suitable for everyday wear
Topaz	Topaz	8	In a protective setting	Perfect cleavage and poor toughness: GIA warns a hard blow might split it
Emerald		7.5 to 8	In a protective setting	Tends to have and surface-reaching fractures
Aquamarine and morganite	Beryl	7.5 to 8	Yes, with care	The same mineral as emerald
Quartz: amethyst, citrine, rose quartz, smoky quartz, tiger’s eye	Quartz	7 (tiger’s eye 6.5 to 7)	Now and then	Quartz is the Mohs reference mineral for 7
Garnet	Garnet group	6.5 to 7.5	Now and then	Varies by species
Zircon	Zirconium silicate	6 to 7.5	Now and then	A natural mineral, not cubic zirconia; GIA gives 6 to 7.5 from low to high types
Jade	Jadeite (6.5 to 7) or nephrite (6 to 6.5)	6 to 7	Now and then	Exceptionally tough, though it scratches more easily than sapphire
Tanzanite	Zoisite	6 to 7	With care	Cleavage and fair to poor toughness: avoid hard blows
Moonstone	Orthoclase feldspar	6 to 6.5	Pendants and earrings are safer	Cleavage and poor toughness; GIA says it is usually set in pendants, earrings and pins rather than rings
Opal	Hydrated silica	5 to 6.5	Pendants and earrings are safer	Very poor to fair toughness; needs care so it does not scratch or break
Turquoise	Hydrated copper aluminium phosphate	5 to 6	Pendants and earrings are safer	Porous; GIA calls it fairly soft
Glass	Glass	5 to 6	No	Can be made to look like almost any gem
Fluorite	Calcium fluoride	4	No	The Mohs reference mineral for 4
Malachite	Copper carbonate	3.5 to 4	No	Soft, with a perfect cleavage

Is moissanite harder than sapphire?

Yes. Moissanite is 9.25 and sapphire is 9, and the real difference is larger than a quarter step suggests. A 1997 study in GIA’s research journal explains that the Mohs scale is disproportionately compressed above 8. On the Knoop scale, a linear measure of indentation hardness, the gap between corundum and moissanite is larger than the gap between corundum and topaz. Both are hard enough for daily wear; the bigger visible difference is fire, and the same study lists moissanite’s dispersion as 0.104 against 0.018 for corundum. See moissanite vs white sapphire. Cubic zirconia, at 8 to 8.5, is softer than both, and GIA notes it is more prone to scratches and abrasions over time; see moissanite vs cubic zirconia.

What is the difference between hardness and toughness?

Hardness is resistance to scratching. The Mohs scale, introduced in 1812 by the German mineralogist Friedrich Mohs, ranks ten reference minerals by which scratches which: talc 1, gypsum 2, calcite 3, fluorite 4, apatite 5, orthoclase 6, quartz 7, topaz 8, corundum 9 and diamond 10. A harder material scratches a softer one, and GIA notes that only a diamond can scratch a diamond. The scale is a ranking, not a measurement, so its steps are not equal. Toughness is resistance to chipping and breaking, and it does not follow hardness. Diamond has cleavage directions, where its atoms are farthest apart, and GIA warns that even a cut diamond can be cleaved by a hard blow, during setting or while it is being worn. GIA’s 1997 moissanite study rated diamond’s toughness good to excellent and moissanite’s excellent, and found no prominent cleavage in moissanite. Topaz, at 8, has a perfect cleavage, which GIA says gives it poor toughness: a hard blow might split it. Jade is the opposite case: at about 6 to 7 it scratches more easily than sapphire, yet GIA explains that its tiny interlocking mineral crystals make it exceptionally tough. Emerald, at 7.5 to 8, tends to have inclusions and surface-reaching fractures that GIA says make it more delicate and prone to damage without careful handling.

Which gems suit an everyday ring?

GIA’s rule of thumb is that gems of 7 or higher are durable enough for rings, and those of 8 or above are ideal for everyday wear, such as engagement rings. That makes diamond, moissanite, ruby, sapphire, alexandrite and spinel the safest choices for a ring worn every day. Topaz and cubic zirconia also reach 8 but need more care: topaz because its cleavage makes it easy to split, so GIA says jewellers prefer protective mountings, and CZ because it scratches over time. Emerald, aquamarine and morganite (all beryl, 7.5 to 8) wear well with care, and GIA recommends highly protective settings for emerald worn every day. Quartz gems such as amethyst and citrine meet GIA’s threshold of 7 for rings but fall short of the 8 it calls ideal for daily wear. Tanzanite, moonstone, opal and turquoise sit below or at the bottom of that line. GIA notes that moonstone is usually set in pendants, earrings and pins rather than rings, that tanzanite needs care to avoid hard blows, and that opal needs care so it does not scratch or break, so pendants and earrings suit these four better than a ring worn every day. A lab-grown ruby, sapphire, spinel or diamond is the same mineral as the mined gem, with the same hardness: US Federal Trade Commission guides allow a lab-grown stone to carry a natural stone’s name only if it has essentially the same optical, physical and chemical properties. A simulant is not, so a glass "ruby" scratches like glass; see lab-created vs simulated, and the key facts table for and fire.

Frequently Asked Questions

What is the second hardest gemstone?

Moissanite, at 9.25 on the Mohs scale, is the hardest gem after diamond, but all moissanite used in jewellery is made in labs. Among natural gems, ruby and sapphire (corundum, 9) come second to diamond.

Is the Mohs scale linear?

No. It only ranks which mineral scratches which. GIA notes that diamond (10) is about four times harder than sapphire (9), and a 1997 study in GIA’s research journal found the scale disproportionately compressed above 8.

Can a diamond chip?

Yes. Diamond is the hardest gem, but hardness only measures resistance to scratching. Diamond has cleavage directions, and GIA warns that a hard blow can cleave a diamond, during setting or while it is being worn.

Is cubic zirconia harder than sapphire?

No. GIA gives cubic zirconia 8 to 8.5 on the Mohs scale and sapphire 9, and notes that CZ is more prone to scratches and abrasions over time.

Are lab-grown gems as hard as mined gems?

Yes, when they are the same mineral. US Federal Trade Commission guides allow a lab-grown or lab-created stone to use a natural stone’s name only if it has essentially the same optical, physical and chemical properties, so lab ruby and sapphire are 9 and lab diamond is 10. Simulants are different materials: glass sold as a gem is only about 5 to 6.

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