Introduction to Ruby Corundum

Ruby corundum, characterized by its purplish-red color and high hardness, is ideal for making cutting tools. Most ruby corundum available today is synthetic.

What is Ruby Corundum?

• The main component of ruby corundum is α-alumina, also known as chromium corundum or ruby.
• In the market, ruby corundum is generally synthetic.
• Ruby corundum is produced by adding 22% chromium to white corundum and melting it in an electric arc furnace, resulting in a purplish-red color.
• Its hardness is slightly higher than brown corundum and similar to white corundum, with a microhardness of 2200-2300 Kg/mm².
• It has higher toughness than white corundum but is slightly less tough than brown corundum.
• Tools made from ruby corundum are suitable for grinding high-carbon steel, high-speed steel, and thin-walled parts.
• The abrasive can also be used for grinding, polishing materials, precision casting sand, coating materials, chemical catalyst carriers, special ceramics, and advanced refractories.

Differences Between Ruby Corundum and Ruby

• Ruby corundum has a purplish-red color and high hardness, making it suitable for cutting tools.
• The main component of ruby corundum is α-alumina, commonly known as chromium corundum.
• Ruby corundum's hardness is higher than brown corundum and its toughness is higher than white corundum.
• Tools made from ruby corundum are ideal for grinding high-carbon steel, high-speed steel, and thin-walled parts.
• Ruby corundum is essentially natural, unprocessed ruby.
• Rubies are corundum gemstones with a red, deep red, slightly purplish-red, or orange-red color. Their main component is aluminum oxide.
• Rubies are extremely hard, second only to diamonds.
• The chemical composition of rubies includes aluminum oxide with trace amounts of chromium, iron, and titanium. The presence of chromium gives rubies their red to pink color.
• Color distribution in rubies is often uneven, forming color bands or patches.
• Ruby crystals are commonly barrel-shaped, short prismatic, or tabular, often with straight growth patterns. Aggregates are typically granular or dense.
• Rubies have a hardness of 9, just below that of diamonds, and exhibit no cleavage but do show fractures.
• Their density ranges from 3.95 to 4.1 g/cm³, with a specific gravity of 3.97-4.05. Rubies are transparent to semi-transparent with a glassy luster.
• They have a refractive index of 1.76-1.77, birefringence of 0.008-0.010, and exhibit strong pleochroism.
• Under long and short-wave ultraviolet light, rubies with high chromium content display red or dark red fluorescence.
• The visible light absorption spectrum of rubies shows prominent absorption lines at 694.2 nm and 682.8 nm in the red region, a broad absorption band from 620 to 540 nm, and weak absorption lines at 468.5 nm.

Applications of Ruby Corundum

• The primary chemical component of corundum is aluminum oxide.
• Formed under high-temperature conditions in the mantle, it emerges on the surface with volcanic activity.
• Corundum comes in a variety of colors, including red, orange, yellow, green, blue, and purple.
• Its hardness is second only to diamonds.
• Corundum is mainly used in high-grade grinding materials, watch and precision machinery bearings.
• Corundum minerals primarily include ruby and sapphire.
• Common corundum products include corundum tubes, corundum bricks, corundum crucibles, brown corundum, corundum powder, corundum sand, corundum balls, ruby corundum , zirconium corundum, white corundum, blue corundum, black corundum, corundum ceramics, corundum micro-powder, and corundum sandpaper.
• Corundum forms through the contact metamorphism of aluminous igneous rocks and limestone or the regional metamorphism of aluminous, silica-poor rocks.
• It is commonly found in crystalline limestone, mica schist, and gneiss, as well as in syenite, nepheline syenite, pegmatite, and basalt.
• Due to its high hardness and weather resistance, corundum is often found in placer deposits.
• Non-gem quality corundum has been used as an abrasive, commonly known as emery, mainly found in Greece, the United States, and Australia. Gem-quality corundum, including ruby and sapphire, is primarily sourced from Sri Lanka, Thailand, and Cambodia.
• Corundum forms under high-temperature, aluminum-rich, silica-poor conditions.
• In endogenous processes, it occurs in aluminum-rich, silica-poor igneous rocks and pegmatites, often coexisting with feldspar and spinel.
• In metamorphic processes, it is found in gneisses associated with skarn, magnetite, and muscovite, or in contact zones between igneous rocks and limestone, coexisting with calcite, magnetite, and epidote, resulting from silica reduction in igneous rocks.
• Corundum belongs to the trigonal crystal system, commonly forming well-shaped hexagonal prismatic or barrel-shaped crystals, with striations or horizontal lines on the prismatic faces, and sometimes triangular cleavage marks on the basal planes. Aggregates are granular.
• Corundum exhibits high-temperature resistance, corrosion resistance, and high strength, with a hardness second only to diamonds.
• It has a high melting point and excellent high-temperature insulation, making it an excellent refractory material.
• Corundum products have good airtightness, making them highly useful in vacuum environments.
• Their excellent high-temperature properties and mechanical strength make them widely used in metallurgy, machinery, chemical, and electronic industries.
• Ruby corundum has powerful, intense energy that is long-lasting.
• It can supplement blood and energy, treat cold hands and feet, and boost courage and confidence in shy, timid, or introverted individuals, enabling them to express themselves boldly.
• Public relations or sales personnel can wear it to increase persuasiveness, personal charm, and leadership qualities, improving interpersonal relationships and enhancing confidence.
• Ruby corundum's prosperous energy promotes health and longevity.

Identifying Ruby Corundum

• Red Glass: Using red glass to imitate ruby is common. Rubies are purplish-red, bright but not glaring, and comfortable to look at, while red glass is bright red and very flashy. Glass is much softer and less dense than ruby, often with surface scratches. Red glass is homogeneous with no pleochroism and shows bubbles under magnification.
• Red Garnet: Garnet is usually brownish-red, less bright, and not as lustrous. Under a polariscope, garnet shows no light and dark changes. Under UV light, rubies fluoresce red, while garnet is inert. The absorption spectrum of garnet is distinct from ruby.

Natural Ruby Corundum Deposits

• Ruby corundum primarily occurs in metamorphic marble deposits, calcite-rich pegmatites, high-grade metamorphic schist, and granulite deposits.
• Notable sources include Mogok in Myanmar, Afghanistan, the Pamir region of the former Soviet Union, northern Hunza in Pakistan, Thailand, and Vietnam.