Buying guide

Sapphire

Sapphire is corundum in every colour except red. Velvety cornflower blue carries the highest premium, but yellow and purple sapphires offer far more colour per euro and are dramatically under-priced relative to blue.

Sapphire at a glance

Mineral family: Corundum
Chemical formula: Al2O3
Mohs hardness: 9
Refractive index: 1.762 - 1.770
Specific gravity: 4.00
Crystal system: Trigonal
Colours: blue, yellow, purple, pink
Birthstone month: September
Anniversary: 5th & 45th
Typical treatment: Heat treatment is standard and stable. Diffusion and beryllium treatment exist and materially reduce value, always require disclosure.
In stock now: 10 stones from $77.50

What drives the price

In one line: Colour saturation and evenness, treatment, origin, size.

Treatment

Heat treatment is standard and stable. Diffusion and beryllium treatment exist and materially reduce value, always require disclosure.

Any seller unwilling to state treatment in writing is telling you something. Every listing on this site states it.

Durability and daily wear

One of the toughest gems available. Ultrasonic and steam safe for untreated and heat-treated stones.

Mohs 9, trigonal crystal system, specific gravity 4.00.

Tradition and meaning

Linked to wisdom, clarity of thought and truthful speech. Blue sapphire is worked with at the throat chakra.

Birthstone for September. Associated with Virgo and Libra. Anniversary stone: 5th & 45th.

Frequently asked

Are sapphires only blue?

No. Sapphire is the name for all gem corundum other than red, which is called ruby. Yellow, purple, pink, green, orange and colourless sapphires are all natural and all correctly called sapphire.

Is sapphire good for an engagement ring?

It is arguably the best non-diamond choice. At Mohs 9 it is second only to diamond in scratch resistance, it has no cleavage plane, and it tolerates daily wear better than emerald, opal or tanzanite.

What is purple corundum?

Purple corundum is purple sapphire. Sellers sometimes use the term corundum when a stone has not been laboratory-certified as sapphire, or to describe material with a colour that sits between pink and purple.