Corundum is a crystallized structure of the aluminum oxide (Al2O3) and one of the most significant minerals in gems. It is the parent mineral species of two of the most renowned precious gemstones in the world, namely ruby and sapphire.

In simple terms:

Red corundum is called Ruby

The remaining colorations of gem quality corundum are referred to as Sapphire.

The information about corundum is critical to every person who is keen on the quality of natural gemstones.

Scientific Definition of Corundum

Corundum: The crystalline form of silicate of Aluminum.

Technical and mineralogical characteristics

According to its technical and mineralogical characteristics, corundum is characterized by the following:

Chemical Formula: Al2O3

Composition: Aluminum oxide

Color: Numerous colours, such as blue, red, violet, pink, green, yellow, orange, gray, white, colourless, black. Sometimes also in shades of a multicolor or striped pattern.

Streak: White

Hardness: 9

Crystal System: Hexagonal

Crystal Forms and Aggregates: Crystals are formed in the form of hexagonal prismatic and tablet crystals, and in the shape of hexagonal bipyramids, the wider at the center, and narrow at the extremities. The crystals tend to be slender and striated transversely and occasionally exist in slender sheets. The edges of the crystals are usually smooth or rounded as a result of alluvial action. As well as likening rounded, waterworn alluvial pebbles, modified octahedrons, massive and as barrel-shaped hexagonal crystals. The crystals are occasionally etched or striated.

Transparency: Transparent opaque.

Specific Gravity: 3.9 - 4.1

Luster: Vitreous to adamantine.

Cleavage: None, and usually shows rhombohedral and basal parting.

Fracture: Uneven

Tenacity: Brittle

Others ID Marks:

1) May fluoresce in shortwave ultraviolet light with either orange, yellow, or red.

2) May be triboluminescent.

Complex Tests: Not soluble in acids.

In Group Oxides: Simple Oxides.

Striking Characteristics: Great hardness, high specific gravity, characteristic crystal form.

Environment: In changed metamorphic rocks, like marble and hornfels, in nepheline syenite pegmatites, and in placer deposits.

Type of rock: Igneous, Sedimentary, Metamorphic.

Popularity (1-4): 1

Prevalence (1-3): 2

Demand (1-3): 1

The second hardest natural mineral on the earth is corundum that is only overtaken by diamond.

The Transformation of Corundum to Ruby and sapphire.

Pure corundum is colorless. The broad range of colors possessed by ruby and sapphire is provided by the trace elements included in the crystal structure:

Chromium - Red color - Ruby

Iron+Titanium - Blue colour - Blue Sapphire.

Iron Yellow or green sapphires.

Vanadium - Purple sapphires

Different shades - Pink, orange and fancy sapphires.

Thus, ruby and sapphire are not other minerals, but merely varieties of the same mineral: corundum, but of different colour.

These are the types of Gemstones that are formed out of Corundum.

The corundum gives rise to a number of valuable types of gemstones:

Emery - Black, heavy type of Corundum, and its color is due to mixture of Magnetite and Hematite and Spinel.

Padparacha- Orange-pink gem variety of Sapphire. Padparadschah is a very rare and demanded variety.

Ruby - Pink -red form of Corundum.

Sapphire - Sapphire is a collection of all types of gems of Corundum and not the red type of Corundum, which is referred to as Ruby. In a gem trade, it is a gem variety specially of Corundum of blue color unless an initial is added to sapphire (i.e. Green Sapphire). Any sapphire with a color other than blue is referred to as a fancy in the gem business.

Star Ruby - Ruby which has the asterism of a star with six rays.

Star Sapphire - Sapphire that has been affected by asterism taking the shape of a six-rayed star.

Ultralite - Wrong in the gem trade Sometimes used to describe blue Sapphire.

These gemstones have a common chemical and physical basis of corundum.

Geological Formation of Corundum

The formation of corundum comes about in the condition of extreme geology as applied to high heat and pressure. It is commonly found in:

• Marble and schist, which are metamorphic rocks.
• Basalt-related deposits
• Alluvial river gravels
• Hydrothermal veins

Noteworthy Localities of Corundum

Well known corundum mining areas are:

• Pakistan – Batakundi and Basal mines
• Myanmar (Burma)
• Sri Lanka (Ceylon)
• Thailand
• Mozambique
• Madagascar
• Afghanistan and Tajikistan

Corundum Gemstones durability

The reason why corundum is so popular, in both form of ruby and sapphire, is that corundum is highly durable.

Corundum gemstones are hard, with a value of 9 on Mohs scale.

These are:

• Very scratch-resistant.
• Awesome as everyday jewellery.
• Appropriate engagement rings.
• Durable and quality products.

This renders corundum to be the most viable and long lasting colored gemstone family.

Treatments in Corundum Gemstones

Ruby and sapphire in turn are of the corundum family, and may be subjected to other industry-accepted treatments:

• Heat Treatment- To enhance color and clearness
• Diffusion Treatment To change surface color.
• Fracture Filling (primarily rubies)

Most precious and rare are the untreated / Natural Stones.

At Kashmir Stones, there is complete disclosure in terms of treatment status of all the corundum gemstones.

The factors of Corundum Quality Grading

All corundum gemstones, be it ruby or sapphire are graded on:

• Color: The most valuable value consideration.
• Clarity Natural inclusions are prevalent.
• Cut: Deciphers brilliance and beauty.
• Carat Weight: Bigger stones are more rare.
• Place of origin Kashmir, Burma, Ceylon, etc.
• Treatment: Untreated stones are on premium prices.

Industrial Uses of Corundum

In addition to gemstones, corundum is also susceptible to the industry due to its hardness:

• Grinding tools and abrasives.
• Polishing powders and sandpapers.
• Optical components
• Watch crystals (artificial crystal of corundum / sapphire)

Nevertheless, the most valuable and the most prestigious use is still gem-quality natural corundum.

Corundum Frequently Asked Questions

What is the difference between Sapphire ans Corundum?

Yes. Sapphire is a gem grade type of corundum. However, it is all corundum and not all corundum is sapphire.

Is ruby a type of corundum?

Yes. Ruby is merely a red corundum, which has been coloured by chromium.

Which is more difficult to make - corundum or diamond?

Diamond is harder (Mohs 10). Corundum comes second only after it at Mohs 9.

Are all Corundom stones natural?

No. Corundum can as well be synthetically processed. In Kashmir Stones we are selling only natural corundum gemstones in full disclosure.

Which locality bears the best Corundom?

Well known sources are Kashmir (Pakistan), Burma and Sri Lanka, which have been associated with producing some of the best rubies and sapphires.

Can Corundum be worn on a daily basis?

Yes. The corundum gemstones are very useful as they have a high degree of hardness and durability thus can be worn on a daily basis.

Conclusion - Corundum is the Foundation of Precious Gemstones.

Corundum is among the most significant minerals in the gemology world. It forms the basis of scientific discovery of both ruby and sapphire- two of the most sought after, toughest and most desired gemstones on Earth.

Corundum gemstones are perfect in highly jewelled work, engagement rings, investment jewellery and works of heirloom quality due to its great hardness, colourful colours, and geological shortage.

Be it the search after the brightest natural sapphire, or the search after the finest natural ruby, knowing corundum will make you make inappropriate and assured buying choices.

We are Kashmir Stones, the specialty of genuine, environmentally friendly, and responsible sourced natural corundum gemstones, where the source is disclosed to the world, and the product is shipped worldwide.