Ruby Gemstones – Properties, Origins, Treatments and Buying Guide

Ruby is one of the most valuable and historically important gemstones ever discovered. Prized for its intense red colour, exceptional durability and rarity, ruby has symbolised power, protection and passion for thousands of years. From royal crowns to high jewellery, natural ruby remains one of the most desirable gemstones in the world.

In this guide we examine ruby from a professional gemmological and commercial perspective, including its physical properties, mineral structure, treatments, durability, origins and how to identify high-quality natural stones.

What Is Ruby?

Ruby is the red variety of the mineral corundum, composed of aluminium oxide. The red colour is caused by trace amounts of chromium within the crystal structure. When corundum occurs in any other colour, it is classified as sapphire — only red corundum is ruby.

This makes ruby one of the hardest, most chemically stable and most valuable gemstones used in fine jewellery.

Ruby has the chemical formula:

Al₂O₃

It is composed of:

• Aluminium
• Oxygen
• Trace chromium (which creates the red colour)

The higher the chromium content, the richer and more valuable the ruby becomes.

Ruby belongs to the oxide mineral group, specifically the corundum family.

Its crystal system is trigonal, giving ruby exceptional structural strength and stability.

Lustre
Ruby has a vitreous to adamantine lustre, producing intense brilliance.

Transparency
Fine ruby is transparent, while lower grades are translucent.

Refractive index
1.76 – 1.78

Specific gravity
3.97 – 4.05

Ruby ranges from:

• Pinkish red
• True red
• Pigeon blood red
• Deep red
• Brownish red (lower quality)

The finest rubies show a vivid, glowing red with no brown or purple undertones.

Ruby has a Mohs hardness of 9, making it one of the hardest gemstones after diamond.

It has:

• Excellent toughness
• No cleavage

This makes ruby ideal for engagement rings and daily wear jewellery.

Most rubies are heat treated to improve colour and clarity.

Acceptable:

• Heat treatment

Undesirable:

• Glass filling
• Diffusion treatment

Always demand full treatment disclosure when buying ruby.

Ruby is extremely durable but still requires sensible care.

Avoid:

• Harsh chemicals
• Acid cleaners
• Blows from hard surfaces

Safe cleaning:

• Warm water
• Mild soap
• Soft brush

Ultrasonic cleaners are safe for untreated rubies but not for glass-filled stones.

Major ruby sources include:

• Myanmar (Burma)
• Mozambique
• Thailand
• Madagascar
• Tanzania
• Sri Lanka