加工...

Corundum Gemstone: Properties, Meanings, Value & More

刚玉宝石：属性、含义、价值等

该文本是机器翻译的。 显示原件？

Corundum is a gemstone family encompassing ruby and sapphire. If you’ve ever wondered what gemstone is corundum, any ruby or sapphire gem or subtype counts.

How rare is corundum? The mineral is common, but gem-quality corundum is rare. Ruby is the rarest type, while blue sapphires are the most common. 

The corundum sapphire is the state gemstone of Montana, USA, and Queensland, Australia. Blue sapphire is Sri Lanka’s national stone, while Myanmar and Thailand honor the corundum ruby as their national stone. 

This guide covers all the meanings, prices, history, and properties of corundum gemstones. 

About Corundum Stone

Firstly, is corundum a precious gem? Yes! It’s half of the list, as ruby and sapphire are two of the four precious gems. 

Ruby is the traditional July birthstone. Sapphire is the traditional birthstone for September. White sapphire is also an April birthstone. 

Astrologically, ruby is a zodiac stone for Cancer and Capricorn. Blue sapphire benefits Virgo and all sapphires benefit Taurus and Libra.  

For wedding anniversary gems, ruby commemorates the 15th, 40th, 52nd, and 80th anniversaries. Similarly, sapphire commemorates the 5th, 45th, and 75th anniversaries. 

Outside of celebrations, what is corundum used for?

Corundum Uses

Corundum’s primary industrial application is for abrasives. Because corundum hardness ranks at 9 on the Mohs scale, it’s useful for making sandpaper, emery boards, grinding wheels, and other polishing tools. 

Most corundum mined is only industrial-quality. Since the first synthetic sapphires of 1902, sapphires have also gained applications in:

• Windows

• Satellite communication

• Scientific tools

• Integrated circuits

Corundum Specifications & Characteristics

As an aluminum oxide mineral, the corundum formula is Al2O3. Iron, chromium, vanadium, and titanium are common impurities. 

Corundum often forms barrel-like, bi-pyramidal, or unterminated prismatic crystals. Otherwise, it’s granular, massive, or pebble-like.

Some properties — namely refractive indices, birefringence, and density — depend on the source. For instance, different-colored sapphires from Australia can each have different properties. 

The highest possible density is 4.06 in reddish-brown sapphires from the Umba River Valley. The lowest possible is 3.80 in Yugoslavian rubies.

Green sapphires tend to have the highest refractive indices, reaching 1.779. The lowest possible value is 1.757 in Sri Lankan blue sapphires. 

Here are corundum’s properties:

• Mohs hardness: 9

• Color: Ruby - Pinkish-red to dark red; Sapphire - Every other color, including colorless, white, gray, blue, blue-green, green, violet, purple, orange, yellow, yellow-green, brown, golden amber, peachy pink, pink, and black

• Crystal structure: Hexagonal (trigonal)

• Luster: Vitreous (glassy) to adamantine; Vitreous to sub-adamantine (polished); Vitreous (fracture)

• Transparency: Transparent to opaque

• Refractive index: 1.757-1.779; Lowest = Sri Lankan blue sapphires; Highest = Sri Lankan green sapphires

• Density: 3.98-4.10

• Cleavage: None

• Fracture: Conchoidal or irregular/uneven

• Streak: White

• Luminescence: Fluorescence & X-ray colors present; Rubies - Varies by source, often red, orange-red, or pink; Sapphires - Sometimes fluorescent and varies by color and source, some red or yellow-orange in X-ray

• Pleochroism: Present and very strong in colored stones; Ruby - red/purplish-red to orange-red; Sapphire - Varies by stone color

• Birefringence: 0.008-0.009

• Optical effects: Asterism - Ruby & sapphire; Color change - Sapphire; Chatoyancy - Ruby & sapphire

• Dispersion: 0.018

Types of Corundum

Each corundum stone comes with its own subtypes. 

Pictured above: Star ruby

Rubies

All red corundum is ruby while all other colors are sapphires. 

The ruby subtypes are:

• Pigeon Blood Ruby: Vibrant red variety with no undertones

• Star Ruby: Ruby displaying asterism, a six-rayed star of light on its surface

• Geneva Ruby: The oldest synthetic gemstone, created around 1885

• Verneuil Ruby: Synthetic ruby created via flame fusion (a.k.a. Verneuil process)

• Flux-Grown Ruby: Synthetic ruby created by dissolving aluminum oxide in a melted flux, followed by ruby crystallization

Among synthetic ruby processes, the verneuil (or “flame fusion”) method is the most common and cost-effective. 

Notable sources may attach their name, such as “Burmese ruby” or “African ruby.”

Pictured above: Padparadscha sapphire

Sapphires

Unlike ruby, sapphires come in lots of colors. Blue corundum is sapphire, but the colors of sapphires encompass the entire rainbow. 

The sapphire subtypes are:

• Color-Change Sapphire: Variety that changes color under different lighting (usually blue to violet, but gray- or greenish-blue to brownish-red are best)

• Star Sapphire: Variety displaying asterism with 6- or 12-rayed star

• Padparadscha Sapphire: One of the rarest types, a pink- to peach-colored variety resembling lotus flower coloring

• Kashmir Sapphire: Most valuable sapphires (no longer mined), with vibrant blue and velvety appearance

Corundum Meaning & History

Ruby symbolizes protection, passion, and manifestation, sometimes called “Stone of Prophecy.” Sapphire symbolizes new love, prosperity, and commitment. Golden sapphire specifically represents wisdom, abundance, and spiritual power. 

Similarly, corundum has religious and secular folklore going back centuries.

Ancient Persians believed sapphires came from a pedestal balancing Earth. Kings wore sapphire for protection, while clergymen wore blue sapphires symbolic of heaven.

Biblically, ruby and sapphire appear among the twelve stones in the High Priest’s Breastplate. Sapphire also appears in the twelve “foundation stones” of New Jerusalem.

In multiple Indian religions, the Navaratna (or “nine gems”) is a beneficial, often astrological, talisman containing both yellow sapphire and ruby. Islamic beliefs claim the first man, Adam, created rubies in Sri Lanka after he was banished from the Garden of Eden.

That’s just scratching the surface, as folklore surrounding rubies and sapphires spans dozens of cultures and time periods.

History

The name “corundum” came long after “ruby” and “sapphire,” derived from the Sanskrit kuruvinda, meaning “ruby.” The first usage (spelled “corinvindum”) came from English naturalist John Woodward in 1725. The current spelling came from Irish geologist Richard Kirwan in 1794. 

Corundum’s first discovery is unclear, but rubies go back to 2500 BC at the latest, based on archeological finds in Myanmar. The oldest known record of sapphires goes back to ancient Etruscans of present-day Italy in 600-700 BC.

Sri Lanka was the most significant corundum locale historically. Their sapphires gained notoriety when Marco Polo described them in his 13th-century travelog Book of Marvels. 

Since scientific gemstone identification didn’t come until later, many red or blue stones have been mistaken for corundum. For at least 1000 years, spinel was continuously mistaken for corundum, like the red spinel in the legendary “Black Prince’s Ruby.” 

Another famous example is the Delhi Purple Sapphire, a reportedly cursed stone that turned out to be amethyst.

Other genuine corundum stones have gained fame in history and pop culture, like the Asprey & Garrard’s 1998 sapphire Heart of the Ocean necklace imitating the one in James Cameron’s Titanic.  

Corundum Healing Properties

All corundum varieties can function as healing stones. As red gemstones, rubies inherently offer greater motivation, passion, and vitality. The popular blue sapphire joins other blue gemstones in bringing serenity and mental clarity.

Energy healers use ruby as a root chakra stone, establishing protection and security. Sapphires can open any chakra, though blue sapphires are great for the throat chakra, helping you understand and communicate your truth.

What about physical and emotional healing?

Physical Healing

Physically, rubies are popular for treating blood or heart problems. Sapphires are said to treat insomnia and vision issues. Medieval beliefs assigned different healing powers to different fingers to wear sapphire rings on:

• Index (Pointer) Finger: Digestive and respiratory systems

• Middle Finger: Spleen, liver, cognition

• Ring Finger: Circulatory system and kidney

• Little Finger (Pinky): Reproductive system and lower body

Emotional Healing

Corundum gems are believed to protect you from harmful thoughts and encourage self-control. They can also help you handle conflict in relationships and relieve anxiety.  

Corundum Gemstone Properties

Experts grade corundum gemstones based on their color, cut, clarity, carat weight, and treatments. 

Color

Ruby’s red coloring comes from chromium impurities, while each sapphire color derives from different impurities. The most valuable shade is pigeon’s blood ruby.

Despite being the most common color, blue sapphires still fetch high prices because of high demand. Padparadscha sapphires are next-highest in value. Yellow, green, and white sapphires are more affordable. 

Cut

Most gem-quality corundum is faceted, which is most valuable. Star ruby or star sapphire must be cut as cabochons to display the “star” properly. Other cuts include beads, carvings, and raw (uncut) specimens. 

Clarity

Corundum has a Type II colored gemstone clarity grade, meaning a few visible inclusions are normal, except in high-quality gems. Many sellers use diamond clarity grades for corundum.

Most inclusions lower corundum’s value, but hematite or rutile inclusions that create asterism or the velvety look of Kashmir sapphires can boost value. Cat’s eye corundum comes about similarly, though these stones actually have imperfect “star” effects.

Common inclusions or imperfections in natural corundum include:

• Fingerprints (tiny internal tubes filled with liquid)

• Needle-like rutile crossing at 60 degrees

• Hexagonal growth lines

• Crystals (e.g. zircon, orthoclase, calcite, apatite, pyrite, magnetite, biotite, spinel)

Of course, the visibility of inclusions can depend on a gem’s size.

Carat Weight

Ruby gems under 1 carat are widely available, but gems weighing 1 carat or more are significantly pricier. 

Similarly, sapphire price-per-carat increases by carat weight, with those more than 5 carats being rare.

Treatments

There are many common corundum treatments. 

Some improve or change the color, such as dyeing, heating, irradiation, thin film coating, and lattice diffusion. Some of these can also improve clarity (heat) or optical phenomena like asterism (heat or diffusion). 

Other treatments improve durability by filling in imperfections, like flux/fracture healing, oiling, lead glass filling, and other fillings (e.g. dye, glass). Some of these can also improve clarity (fracture healing and lead glass filling) or coloring (other fillers). 

Certain treatments are more common. Thin film coating is the rarest, while heating, fracture healing, and lead glass filling are most common. 

Some are only done on certain subtypes. Lattice diffusion gives light-colored sapphire padparadscha coloring. Diffusion is only common on star ruby and blue sapphire.

You can test for treatments through immersion and/or magnification in all cases except for irradiation, which is undetectable.

Remember: Gemstone sellers should always disclose any gem treatments. Ask for a reputable gemstone certification when buying. 

Corundum Formation & Sources

Corundum forms when aluminum-rich, silica-poor rocks undergo high-temperature metamorphism. 

Miners find the stone in various environments, from metamorphosed dolomite and limestone to placer deposits to igneous rocks like nepheline syenite.

Mining Locations

Though industrial corundum is found worldwide, only some locales produce gem-quality corundum. 

Significant gem-quality sapphire sources are:

• Australia

• Kashmir

• Montana, USA

• Myanmar

• Sri Lanka

• Thailand

Notable gem-quality ruby sources are:

• Afghanistan

• Cambodia

• Kenya

• Madagascar

• Mozambique

• Myanmar

• Nepal

• Sri Lanka

• Tanzania

• Thailand

• Vietnam

Now, how expensive is corundum?

Corundum Price & Value

Gem-quality corundum has high prices but also a broad range, with many high-quality sapphires within financial reach. Of course, price depends on each stone’s properties. 

Ruby Prices

Heat-treated, faceted rubies price rates:

• 0.5 to 1 carat: $150 to $6,500 per carat

• 1 to 2 carats: $300 to $10,000 per carat

• 2 to 3 carats: $450 to $20,000 per carat

• 3 to 5 carats: $700 to $25,000 per carat

• 5+ carats: $1,200 to $35,000 per carat

Next, untreated, faceted Burmese rubies: 

• 0.5 to 1 carat: $550 to $18,000 per carat

• 1 to 2 carats: $1,000 to $35,000 per carat

• 2 to 3 carats: $1,250 to $70,000 per carat

• 3 to 5 carats: $2,500 to $100,000 per carat

• 5+ carats: $4,500 to $180,000 per carat

Ruby cabochons range from $20-$700 per carat, or $4,500 per carat for cabs over 3 carats. Star rubies range from $100-$5,000 per carat. Indian rubies are most affordable at $1-$15 per carat. 

Sapphire Prices

The most expensive are faceted Kashmir sapphires:

• 1 to 2 carats: $2,400 to $22,650 per carat

• 2 to 3 carats: $2,800 to $33,000 per carat

• 3 to 4 carats: $5,000 to $40,500 per carat

• 4+ carats: $17,700 to $51,000 per carat

Now heat-treated, faceted blue sapphires:

• 0.5 to 0.75 carat: $210 to $1,275 per carat

• 0.75 to 1 carat: $330 to $1,500 per carat

• 1 to 2 carats: $900 to $4,500 per carat

• 2+ carats: $460 to $10,500 per carat

Next is faceted, pink (Padparadscha) sapphires:

• 0.5 to 0.75 carat: $140 to $675 per carat

• 0.75 to 1 carat: $50 to $1,050 per carat

• 1 to 2 carats: $110 to $3,300 per carat

• 2+ carats: $825 to $8,400 per carat

Other colors of faceted sapphires:

• Yellow: $50 to $750 per carat under 2 carats; $375 to $1,625 per carat over 2 carats

• Green: $20 to $150 per carat under 2 carats; $30 to $240 per carat over 2 carats

• Purple: $280 to $575 per carat under 2 carats; $1,200 to $1,840 per carat over 2 carats

• White: $50 to $200 per carat (0.5 to 3 carats); $100 to $700 per carat (3 to 5 carats); $500 to $800 per carat (5 to 15 carats)

• Color Change: $120 to $3,000 per carat (0.5 to 1 carat); $300 to $5,000 per carat (1 to 7 carats)

Blue sapphire cabochons range from $20-$300 per carat. Black star sapphires are most affordable at $13-$30 per carat, followed by blue star sapphires at $20-$1,200 per carat. Fancy-colored star sapphires go for $100-$500 per carat. 

Corundum Care and Maintenance

Near-diamond hardness and no cleavage means corundum gemstone care is easy. Stones with good clarity and no treatments (besides heat) are the easiest, but be careful with treated, heavily-included, or fractured gems — you may want protective settings for jewelry made with these vulnerable types. 

Only clean vulnerable corundum with warm water, mild soap, and a soft toothbrush. Avoid ultrasonic or steam cleaners, along with harsh chemicals. Other corundum stones can be cleaned with mechanical cleaners.

Captivated by Corundum? 

If corundum captivates you, you’re not alone — these gems have enchanted people for ages. With various different colors and benefits, the only dilemma is choosing your favorite!

Explore our ruby and sapphire corundum gemstones today!

Ruby

Sapphire