Corundum Mineral: Ruby, Sapphire, Hardness, Properties and Uses

Corundum is one of the most important gemstone minerals in the world. It is the mineral family that includes two of the most famous gemstones in jewelry: ruby and sapphire. Known for its brilliance, durability, and wide variety of colors, corundum has been prized for centuries in fine jewelry, gem collecting, and decorative art.

From a gemology perspective, corundum combines beauty with exceptional durability. It ranks 9 on the Mohs hardness scale, making it one of the hardest natural minerals on earth. Only diamond ranks higher. This durability is one reason ruby and sapphire are ideal gemstones for rings, earrings, pendants, and other jewelry designed for everyday wear.

The chemical formula of corundum is Al₂O₃ (aluminum oxide). Pure corundum is colorless, but trace elements create vivid gemstone colors. Chromium produces red ruby, while iron and titanium create blue sapphire. Other trace elements produce yellow, pink, purple, green, and orange sapphire varieties.

What Is Corundum?

Corundum is a naturally occurring mineral formed in metamorphic and igneous rocks. Ruby and sapphire are both varieties of corundum, meaning they share the same mineral composition but differ in color.

Ruby is the red variety of corundum. Sapphire refers to all other colors of gem-quality corundum, although blue sapphire is the most famous. Because ruby and sapphire share the same mineral structure, they have similar hardness and durability.

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Corundum Chemical Composition

Corundum is composed of crystallized aluminum oxide. Its dense crystal structure gives it exceptional hardness and scratch resistance.

• Chromium produces red ruby
• Iron and titanium create blue sapphire
• Iron may produce yellow or green sapphire
• Trace element mixtures create pink, purple, orange, and other fancy sapphires

Types of Corundum Gemstones

Ruby – The Red Variety of Corundum

Ruby is the red variety of corundum and one of the most valuable colored gemstones. Fine rubies display vivid red color with strong saturation and transparency.

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Sapphire – All Other Colors of Corundum

Sapphire includes all non-red corundum gemstones. Blue sapphire is the best known, but sapphires also occur in yellow, pink, green, purple, white, and orange.

One rare variety is padparadscha sapphire, which displays a unique pink-orange color.

Browse our sapphire engagement rings and sapphire rings.

Corundum Hardness and Durability

Corundum ranks 9 on the Mohs hardness scale, making ruby and sapphire extremely resistant to scratches. This durability makes them excellent gemstones for everyday jewelry.

• Engagement rings
• Wedding jewelry
• Anniversary gifts
• Earrings and pendants
• Statement rings

Corundum vs Diamond Hardness Comparison

Diamond is the hardest natural mineral, but corundum is very close behind and still extremely durable.

Gemstone	Mohs Hardness	Durability
Diamond	10	Excellent for everyday wear
Corundum (Ruby / Sapphire)	9	Excellent for everyday wear
Topaz	8	Good durability
Quartz	7	Moderate durability
Opal	5.5–6.5	More delicate

Where Corundum Is Found

Major corundum deposits exist in:

• Sri Lanka
• Myanmar
• Thailand
• Madagascar
• India
• Tanzania
• Australia

Natural vs Synthetic Corundum

Corundum may occur naturally or be created in laboratories. Synthetic ruby and sapphire share the same chemical composition but are grown under controlled conditions.

Explore other modern gemstone options such as lab grown diamond rings.

Uses of Corundum

Besides jewelry, corundum is used industrially because of its hardness.

• Abrasive powders
• Grinding wheels
• Polishing compounds
• Watch crystals
• Optical components

Frequently Asked Questions

What is corundum?

Corundum is a mineral composed of aluminum oxide that forms the gemstone varieties ruby and sapphire.

How hard is corundum?

Corundum ranks 9 on the Mohs hardness scale.

Is sapphire corundum?

Yes. Sapphire is any non-red variety of corundum.

Is ruby corundum?

Yes. Ruby is the red variety of corundum.

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