Sapphire Hardness and Durability: The Complete Guide

Sapphire is 9 on the Mohs hardness scale, out of 10. That number answers one question only: what can scratch your stone? Ruby gets the same 9, because ruby and sapphire are one mineral, corundum. Pick two materials below: which marks the other?

The rule is short: a mineral scratches anything ranked the same or lower. So your sapphire scratches topaz, emerald, quartz and another sapphire. Among natural gems, only diamond scratches it back.

On your hand, that matters. Dust and sand are mostly quartz, which ranks 7. A gem ranked below topaz can pick up scratches over time, however careful you are. Sapphire sits one rank above topaz.

One trap: Mohs is a ranking, not a measurement. Diamond is not one tenth harder than sapphire. It is far harder.

Yes. Hard does not mean unbreakable. Resisting chips, cracks and breakage is another quality: toughness. Topaz shows the difference. It is hard, yet it breaks rather easily if it is hit in the right place. Touch a point on the chart below.

Sapphire is strong on both counts. It has no cleavage, the flat plane of weakness along which a topaz or a diamond can split. Its toughness is rated excellent: the same grade as chrysoberyl, one step below jade. What can lower it in your stone? Large fractures or inclusions, heavy twinning, and some treatments. Black star sapphire is the usual example, a twinned stone that can part along a flat plane.

Once it is on your hand:

• Heat. High heat can change the color or the clarity. Before any repair with a torch, tell your jeweler what the stone is.
• Light. Generally stable.
• Cleaning. Warm, soapy water is safe. Ultrasonic and steam cleaners usually are too, but never for a fracture-filled or cavity-filled stone.
• The setting. Precious metals are relatively soft, and a stone that is loose in its mount can wear through a prong. Have the prongs checked.
• Storage. Your sapphire scratches softer gems. Keep it apart from them in the jewelry box.

For a ring you never take off, read our guide to sapphire engagement rings.

Some treatments do, and this is the question to ask before the Mohs one. The hardness of sapphire stays at 9. What changes is how stable the stone is. Read the ladder below, top to bottom.

So ask which treatment, and get the answer in writing. Heat has its own page: unheated vs heated sapphire. Detecting a treatment is laboratory work, and a report from an independent outside laboratory can follow your purchase. Here is what a gemstone certificate proves.

Yes. Blue sapphire hardness, pink sapphire hardness, yellow, teal: the answer is 9 every time. Sapphire is any corundum that is not red; the red one is ruby. Blue is the classic. Everything else is called fancy sapphire: violet, green, yellow, orange, pink and purple, the colorless stones sold as white sapphire, the pinkish orange padparadscha, plus parti-colored and color-change stones. Below, one stone from our stock per color.

Lab-grown? Same answer. A synthetic sapphire has essentially the same chemical composition, crystal structure and properties as a natural one, hardness included.

Want the colors themselves? Go to our guide to sapphire colors or, for blue alone, to cornflower vs royal blue.

My view: hardness never decides between two sapphires, because they all have the same. Let's be honest, it is the reassuring part of the purchase. Your money goes on four other things.

• Color. Nothing weighs more on the value of a blue sapphire. The most valued stones are a velvety blue to violetish blue, medium to medium-dark in tone, with strong to vivid saturation.
• Treatment. Heated or not, diffused or not: go back to the ladder above.
• Origin. Kashmir, Myanmar and Sri Lanka are the three historic sources, known for the finest blue sapphires. Thailand, Cambodia, Australia and Madagascar supply the bulk of commercial quality, and Madagascar emerged in the 1990s as a significant source of good to fine stones. Find every source on our sapphire origins map; Sri Lanka has its own page, our Ceylon sapphire guide.
• The stone itself. Look for large fractures. They are what can make one sapphire less tough than its reputation.

Curious what sellers ask? See sapphire price per carat. We select loose sapphires one stone at a time, and we can have yours set in a ring made to order.