Precious blue gemstones have been carried and worn as embellishments since ancient times. Symbolizing beauty, honesty, truth and loyalty, blue remains a first-pick color for important gemstone jewelry. The very best transparent, faceted stones combine noticeable, attractive blue color with overall gem toughness that will withstand the rigors of daily wear.
Precious Blue Gemstones for Rings
Due to their exquisite beauty, extreme overall toughness, and ability to hold polish, the gems diamond, sapphire, and spinel are the most suitable blue gems for engagement ring and other daily-wear jewelry. Durability for each gem type is determined by several factors, including gem surface hardness (measured on the Mohs scale of hardness) a gem’s tenacity, and its proclivity to cleave or fracture.
When compared to tough diamond, stones like softer tanzanite, or more brittle zircon, may be subject to surface abrasion or chipping if worn daily without special care. These stones may be better suited as special occasion rings, earrings or pendant jewelry. However, they still make fine, beautiful blue jewelry gems and they may be worn daily as ring stones with care and maintenance.
Diamond: Most Durable Blue Stone
Natural blue diamond, described by the Gemological Institute of America as one of the “fancy” diamond colors, comes in many shades of blue – from barely perceptible pale and delicate hues to rich, complex, deep hues. Many “blue” diamonds are actually gray-blue, grayish blue, blue-gray, or bluish gray. Stones with the “blue” descriptor at the end of the color name, ie, gray-blue, as opposed to blue-gray, are most prized and pricey. Best blue diamonds are lively gems with distinctly blue, saturated, intense color; transparent; and free of visible inclusions.
The hardest of all gemstones, diamond rates top-number 10 on the Mohs hardness scale. This, combined with its other durable qualities, ensure that blue diamond jewelry will last for generations.
Rare Natural Blue Diamonnd Colored by Boron
Colorless diamond is made of carbon. Trace amounts of boron in the carbon creates the appearance of blue. Blue diamond is very scarce and is most usually quite small compared to other gemstones, even other diamonds. As one of the most rare diamond colors, natural blue diamond is extremely pricey. Stones should not be treated, and should be accompanied by a report confirming natural origin from a well-respected lab, like the Gemological Institute of America.
Diamond has superior adamantine luster, is singly refractive – with an extremely high refractive index (RI) of 2.41 – and has relatively high dispersion. Specific gravity for diamond is 3.52. Blue diamonds may be found in fancy shapes, round brilliant cuts, and often radiant cuts that work best at keeping and projecting diamond color.
Although diamonds are extremely tough, brilliant and sparkly, generally speaking, the color of natural blue diamond will not rival the color of blue sapphire in terms of intensity and saturation. However, for the quintessential in gemstone durability, along with great transparency, fire and brilliance, there is no better gemstone than diamond.
Sapphire: Ultimate Blue Gem
Blue corundum commonly known as sapphire, has a well-earned reputation as the ultimate blue gem. Only the more-recently discovered tanzanite rivals sapphire in terms of potential richness and overall saturation of blue color. Sapphire has tanzanite beat, however, in terms of overall gem durability.
Rated 9 on the Mohs hardness scale, sapphire is a wonderfully hard gem, second only to diamond, with a vitreous luster that holds a great polish. Specific gravity is 4, which means a sapphire will be smaller in size than a diamond of the same weight.
Sapphire is made of aluminum oxide and is colored blue by iron and/or titanium. The gem comes in a full-range of blue hues, from extremely light to dark. Highly saturated, medium to medium-dark, pure-blue gems, and gems with a touch of violet in the blue, are most prized.
Doubly refractive, with an RI of 1.76, blue sapphire commonly shows greenish blue to violet-blue pleochroism when viewed from different directions. The pleochroism may be subtle to the eye.
It is acceptable practice to heat-treat sapphire to improve color and clarity. However, any treatments affect value and should be disclosed. Buyers pay a premium for clean, transparent, untreated sapphire. Also, gorgeous gems that show a bit of “silk,” or rutile needles, in the gemstone are highly desirable, especially untreated stones of top color. Inferior sapphire stones will appear lifeless, very dark, blackish, washed out, or show obvious color zoning, inclusions, or windowing.
Sapphire’s Origin Impacts Price
Although fine sapphire is sourced from many places around the world, stones sourced from Kashmir, Myanmar (Burma), Sri Lanka (Ceylon) and Madagascar are most highly valued, and generally in that order. Prices for large, quality sapphire specimens are extremely high. A stone’s place of origin may have great impact on price.
Quality Kashmir stones are known from their distinctive powdery or velvety appearance and blue to violetish blue colors with no green tones. There is no visible green tint in the best Burmese sapphires either. These sapphires are known for evenly distributed, highly saturated, bright, electrifying blue color. Some extinction areas (darkness) may be expected in Burmese stones. The most coveted Burmese sapphires come from the Mogok region.
Best Ceylon sapphires are violetish blue to blue and may show some gray. Color may be lighter and less evenly distributed than Kashmir and Burmese stones, however, Ceylon sapphires are extremely brilliant and show less extinction than other sapphires. Buyers who prefer more transparent, sparkly blue gems, will enjoy quality sapphire from Sri Lanka with the added bonus of having to pay less for them than for quality Kashmir and Burmese stones.
Spinel: Lesser Known, Hard Blue Gemstone
Mistaken as corundum for centuries, beautiful spinel is found in royal jewels around the world. High-quality “pure” blue and cobalt blue spinel gems are a sight to behold and usually cost a fraction of blue sapphire and diamond, even though spinel is much more rare than diamond or sapphire.
Undesirable blue spinel may have too much gray or is too dark or light. A poorly cut, lifeless stone with windowing is not considered quality.
Spinel is composed of magnesium aluminum oxide, and the blue varieties of spinel are colored by iron or sometimes cobalt. Spinel from Myanmar (Burma) is quite coveted, as well as stones from Sri Lanka (Ceylon). There are other fine sources as well.
Spinel and Sapphire Share Sources
Often found alongside corundum in nature, spinel, is relatively similar to sapphire in terms of both its looks and its chemical make-up. Both gem types are formed when impure limestone changes due to heat and pressure. There are however, several important differences between spinel and corundum.
First, spinel, rated Mohs 8, is not as hard as corundum. A most visible difference is that spinel, like diamond and garnet, is one of a few single-refracting gemstones (RI is 1.71). Also, the specific gravity of spinel is 3.60, meaning spinel is larger than a same-weight sapphire and very close to diamond in this regard. Finally, spinel is sold as a totally natural gemstone and is never treated in any way.
Cherished by collectors, spinel is not nearly as well known by the public as sapphire, or as easy to find as sapphire, especially top specimens. However, when it can be found, quality, natural spinel represents a great gemstone value. For now, very rare spinel costs a fraction of similar-quality sapphire. Taking time to seek-out fine blue spinel is well worth the effort to have a very collectible, heirloom-worthy jewel.