Spinel

Category	Semi-precious	Mohs hardness	8
Birthstone	August	Luster	Vitreous
Major sources	Myanmar, Sri Lanka, Vietnam	Care level	Easy
Typical colors	Red Pink Blue

What this gemstone is

Spinel is a magnesium aluminum oxide mineral that crystallizes in the cubic system, forming octahedral crystals. It is a durable gemstone with a Mohs hardness of 8, making it suitable for most types of jewelry, including rings. Spinel occurs in a wide range of colors, including red, pink, blue, purple, orange, and black. Red spinel is particularly prized and has historically been confused with ruby. Unlike ruby, spinel is not pleochroic and typically lacks the strong fluorescence of ruby. Spinel is an allochromatic gemstone, meaning its color is due to trace elements such as chromium, iron, and cobalt. The most valuable spinels are vivid red, often called "flame spinel" or "ruby spinel," and vibrant cobalt blue. Spinel is a single-refractive gemstone, which means it does not show doubling of facets when viewed under magnification. It is often found in alluvial deposits as water-worn pebbles. Spinel is the birthstone for August, along with peridot and sardonyx. It is a popular choice for engagement rings due to its hardness and brilliance.

How it forms and where it's found

Spinel forms in metamorphic rocks, typically in marble and other calcium-rich rocks that have been subjected to high temperatures and pressures. It also occurs in igneous rocks such as basalt and in pegmatites. The formation of spinel requires the presence of magnesium and aluminum, which are common in the Earth's crust. Spinel crystals are often found in association with corundum (ruby and sapphire), calcite, and dolomite. Major sources of spinel include Myanmar (Burma), Sri Lanka, Vietnam, Tanzania, and Madagascar. Myanmar is famous for producing some of the finest red and pink spinels from the Mogok Stone Tract. Sri Lanka is known for its blue, purple, and pink spinels. Vietnam has become a significant source of vibrant pink and red spinel in recent years. Tanzania produces spinel in a variety of colors, including red, pink, and orange. Spinel is also found in Afghanistan, Pakistan, and Tajikistan. The gems are typically recovered from alluvial deposits, where they have been weathered out of their host rocks and concentrated in riverbeds and gravels. Mining methods range from simple panning to mechanized operations.

How to identify it

Spinel can be identified by its physical and optical properties. It has a Mohs hardness of 8, a specific gravity of 3.6 to 3.7, and a refractive index of 1.712 to 1.762. Spinel is singly refractive, meaning it does not show birefringence, which distinguishes it from ruby and sapphire. Under a polariscope, spinel remains dark when rotated, while doubly refractive stones show a blink. Spinel typically has a vitreous luster and may exhibit fluorescence under ultraviolet light, especially red and pink stones. Inclusions in spinel can include octahedral crystals, needle-like rutile, and fingerprint patterns. Natural spinel often contains small mineral inclusions, such as zircon, apatite, or calcite. Synthetic spinel, which is manufactured by the flame-fusion method, can be identified by its lack of inclusions, curved striae, and anomalous double refraction. Spinel can be confused with garnet, ruby, sapphire, and tourmaline. A refractometer and microscope are essential tools for identification. For definitive identification, a gemological laboratory can perform advanced tests such as spectroscopy and chemical analysis.

Value and buying guide

The value of spinel is determined by several factors: color, clarity, cut, and carat weight. The most valuable spinels are vivid red, often with a slight orange or pink hue, and vibrant cobalt blue. Pink and purple spinels are also highly sought after. Color should be evenly distributed and saturated. Clarity is important; spinels with few inclusions and high transparency command higher prices. However, many spinels contain some inclusions, which can affect durability if they reach the surface. Cut quality affects the gem's brilliance and overall appearance. Spinel is cut into various shapes, including oval, cushion, round, and emerald cut. Carat weight also influences value; larger stones are rarer and more expensive per carat. Spinel is not typically treated, but some stones may be fracture-filled or dyed, which lowers value. Prices vary widely depending on quality and size. It is advisable to purchase from a reputable dealer and request a gemological report from a recognized laboratory. For insurance or resale, a professional appraisal is recommended.

Care and cleaning

Spinel is a durable gemstone with a Mohs hardness of 8, making it resistant to scratches and suitable for everyday wear. However, it can be damaged by harsh chemicals or extreme temperature changes. To clean spinel, use warm soapy water and a soft brush. Avoid ultrasonic and steam cleaners, as they can cause fractures to expand or damage the stone if it has inclusions. Do not use chlorine bleach or other harsh chemicals, as they can dull the surface. After cleaning, rinse the gem thoroughly and pat dry with a soft cloth. Store spinel jewelry separately from other gemstones to prevent scratches. Although spinel is tough, it can still chip if struck sharply. Remove spinel rings before engaging in rough activities such as sports or gardening. For professional cleaning, consult a jeweler who is experienced with spinel. With proper care, spinel jewelry can be enjoyed for generations.

Meaning, lore, and birthstone

Spinel has a rich history and has been treasured for centuries. It was often mistaken for ruby; some of the most famous "rubies" in history are actually spinel, including the Black Prince's Ruby in the British Imperial State Crown and the Timur Ruby. The name "spinel" is derived from the Latin word "spina," meaning thorn, referring to its sharp crystal points. In folklore, spinel was believed to protect its wearer from harm and to bring good luck. It was also thought to enhance vitality and to help overcome challenges. Spinel is the birthstone for August, along with peridot and sardonyx. It is also associated with the zodiac signs of Leo and Scorpio. In modern times, spinel is appreciated for its own merits and is a popular alternative to ruby and sapphire. It is given as a gift to celebrate 22nd wedding anniversaries. Spinel is found in many colors, each with its own metaphysical properties. Red spinel is associated with passion and energy, while blue spinel is linked to communication and calm.

Frequently asked questions

Q: Is spinel a ruby? A: No, spinel is a different mineral species. Although they can look similar, spinel is singly refractive and has a different chemical composition. Ruby is a variety of corundum (aluminum oxide), while spinel is magnesium aluminum oxide. Q: Can spinel be treated? A: Spinel is generally untreated, but some stones may be fracture-filled or dyed to improve appearance. These treatments should be disclosed by the seller. Q: How does spinel compare to ruby in terms of value? A: Fine red spinel can be less expensive than top-quality ruby, but prices vary widely based on color, clarity, and size. Some exceptional spinels can command high prices. Q: Is spinel suitable for engagement rings? A: Yes, with a Mohs hardness of 8, spinel is durable enough for engagement rings, though it should be worn with care. Q: How can I tell if a spinel is natural or synthetic? A: Natural spinel typically contains inclusions, while synthetic spinel is often flawless and may show curved striae. A gemological laboratory can provide definitive identification.