Jewelry Education

Gemstones

Sapphire, ruby, and emerald: what separates them, how color is judged, which will survive daily wear, and the treatment questions to ask before you buy.

Colored stones are graded on the opposite principle from diamonds. A white diamond is valued for the absence of color; a sapphire, ruby, or emerald is valued almost entirely for the presence and quality of it.

That makes buying one a different exercise. Here is the short version, followed by the full guides.

Two things worth knowing first

Ruby and sapphire are the same mineral. Both are corundum. Red corundum is called ruby; corundum of every other color is called sapphire. Both rate 9 on the Mohs scale, which makes them the most practical colored stones for a ring worn every day.

Emerald plays by different rules. Visible inclusions are normal rather than penalized, and nearly every emerald is oil-treated. It is softer and more brittle than corundum, so it wants a protective setting and must never go near an ultrasonic cleaner.

The three at a glance

	Sapphire	Ruby	Emerald
Mineral	Corundum	Corundum	Beryl
Hardness (Mohs)	9	9	7.5–8
Typical clarity	Often eye-clean	Usually included	Always included
Common treatment	Heat	Heat; sometimes glass filling	Oil or resin
Daily-wear ring	Excellent	Excellent	With care
Birthstone	September	July	May

If you want one recommendation: for an engagement ring or any piece worn daily, sapphire and ruby are the safe choices. Save emerald for earrings, pendants, and rings you can take off.

The guides

Sapphire

Every corundum color but red. Colors and origins, what Mohs 9 means for daily wear, and how heat treatment affects value.

Read the guide

Ruby

The rarest of the three. Pigeon's blood color, why inclusions are expected, and the treatment question that changes everything.

Read the guide

Emerald

Where the emerald cut came from, why a jardin is normal, what oiling does to value, and how to care for one.

Read the guide

Gemstone color: hue, tone and saturation

The three components that set a colored stone’s value, and how to judge them yourself rather than taking a description on trust.

Read the guide

Before you buy any colored stone

Ask what has been done to it. Heat is routine and permanent. Fracture filling, diffusion, and dyeing are not, and they change the value substantially.
Get a report for anything significant. An independent laboratory document should state treatment, and origin if origin is being claimed.
See it in more than one light. Daylight and ordinary indoor light. A stone that only sings under a spotlight will disappoint at home.
Match the stone to the wear. Hardness decides whether a ring still looks good in ten years.
Think about the metal. Yellow gold warms a stone’s color; white metals keep it crisp. See our precious metals guide.

Find your gemstone

Browse our color stone rings, or talk to a consultant about sourcing a particular stone, color, and certification.

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