Dictionary of Jewelry Terminology


Terminology. Dictionary. Encyclopedia. Jargon. Lingo.

Introduction to Corundum

This article is about, "corundum." We will try to explain what it is, what it does, and how it is used in the jewelry industry.


Corundum is a mineral that comes in many different colors, but the most well-known color is probably red. When corundum is red, we call it "ruby." When it's any other color, we call it "sapphire." So, rubies and sapphires are actually the same mineral, just different colors!

You might see corundum in all sorts of jewelry, like rings, necklaces, and earrings. It's a really hard mineral, which means it's durable and can stand up to everyday wear and tear. That's one reason why it's so popular in jewelry.

In addition to being used in jewelry, corundum is also used in industrial applications. For example, it's used to make things like sandpaper and grinding wheels, because it's so hard and can easily wear down other materials.

So, to sum it up, corundum is a mineral that comes in many different colors, but is most commonly known as rubies or sapphires. It's used in jewelry because it's hard and durable, and can also be used in industrial applications.

More Depth

Corundum is a mineral that is known for its hardness and durability. It is composed of aluminum oxide and comes in a variety of colors, including red, blue, green, yellow, and pink. Corundum is also known as a crystalline form of aluminum oxide, and is often found in metamorphic and igneous rocks.

The most famous varieties of corundum are ruby and sapphire. Ruby is a red corundum, while sapphire can be any other color. For example, blue sapphire is a common variety of sapphire, but sapphire can also be found in colors like yellow, green, and pink. The color of corundum is determined by trace elements within the mineral. For example, the presence of chromium within the crystal structure is what gives ruby its characteristic red color.

Corundum is a very hard mineral, with a Mohs hardness scale rating of 9. This makes it one of the hardest minerals on Earth, and it is only surpassed in hardness by diamond. Because of its hardness and durability, corundum is often used in industrial applications. It is commonly used as an abrasive material, such as in sandpaper and grinding wheels. Additionally, corundum is used as a refractory material, meaning that it can withstand high temperatures and is used in the production of high-temperature ceramics and refractory bricks.

In the jewelry industry, corundum is highly valued for its hardness, durability, and vibrant colors. It is commonly used in engagement rings and other high-end jewelry pieces. When corundum is cut and polished, it can exhibit a stunning brilliance and fire that is prized by jewelers and collectors alike.

In summary, corundum is a mineral composed of aluminum oxide that is known for its hardness, durability, and vibrant colors. It is commonly found in metamorphic and igneous rocks, and is valued in both the jewelry and industrial sectors for its properties. The most famous varieties of corundum are ruby and sapphire, which are highly sought-after for their beauty and rarity.


Class oxides and hydroxide
Crystal system trigonal
Composition aluminum oxide
Habit steep hexagonal bipyramids, or stout columns, or rhombohedra
Refractive index 1.760 - 1.780
Birefringence 0.008
Dispersion 0.018
Specific gravity 3.98 - 4.00
Hardness * 9
Cleavage weak basal parting
Fracture conchoidal
Luster adamantine to vitreous
Notable locations Sri Lanka, Burma (Myanmar), Thailand, Montana in the USA, India, China, Australia, Rwanda, Kenya, Tanzania, Vietnam Madagascar
Color colorless, somtimes with light tints of pink, blue, or yellow, blue (fancy sapphires are any color except red), pinkish orange, light to dark green, shades of pink to purple-pink (magenta), yellow, golden, orange, red to purplish red (star stones may be reddish pink as well)

Back to the Dictionary of Jewelry Terminology.