All About Rubies

One of the most popular traditional jewelry stones, ruby is exceptionally durable. Its colors — always red — can reach vivid levels of saturation. Fine-quality rubies are some of the most expensive gemstones, with record prices over $1,000,000 per carat. However, rubies are also subjected to more treatments than almost any other gem. Treatments are commonplace and expected with Rubies. They will enhance the color and value of the stone.

Burma or Burmese Ruby

This is the traditional color most people think of when we say Ruby. The darkest and most sought after color is aptly (and gruesomely) named Pigeons Blood. As of May 2015, the record price for a ruby is approximately $1.172 million per carat. ($30 million for a 25.59 carat Mogok “pigeon’s blood” ruby). Round, pear and marquis cuts will add about 10% extra to the cost per carat. Emerald cuts can add up to 30% more due to the complexity of the cut.

Large, gem-quality rubies can be more valuable than comparably sized diamonds and are certainly rarer. In fact, smaller blue sapphires (1 to 3 Carats) are relatively abundant compared to small, gem-quality rubies. As a result, even small rubies have relatively high values.

The vast majority of rubies are “native cut” in their country of origin. High-value ruby rough is tightly controlled and rarely makes its way to custom cutters.

Occasionally, such native stones are re-cut to custom proportions, albeit at a loss of weight and diameter. Custom-cut and re-cut stones usually have higher values per carat than native or commercial-cut stones.

The Data About Rubies

Name Ruby
Is a Variety of Corundum
Varieties Flux-Grown Ruby, Geneva Ruby, Star Ruby, Verneuil Ruby
Crystallography Hexagonal (trigonal)
Refractive Index 1.757-1.779
Colors All varieties of red, from pinkish, purplish, orangey, brownish, to dark red.
Luster Vitreous to adamantine
Polish Luster Vitreous to subadamantine
Fracture Luster Vitreous
Hardness 9
Wearability Excellent
Fracture Conchoidal
Specific Gravity 3.99-4.1, usually near 4.
Birefringence 0.008-0.009
Cleavage None
Dispersion 0.018
Heat Sensitivity No
Luminescence Myanmar stones fluoresce intensely, red, in SW, LW, and X-rays. Red fluorescence is, however, not diagnostic of country of origin or natural origin. Thai ruby fluoresces weak red in LW, weak or none in SW. Sri Lankan ruby fluoresces strong orange-red in LW, pink (moderate) in SW. Flame Fusion: very strong in LW, orange/red, moderate to strong in SW, orange/red. Flux Grown: strong in LW, orange/red, moderate to strong in SW, orange/red. (May have blue over-tint)
Luminescence Present Yes
Luminescence Type Fluorescent, UV-Long, UV-Short, X-ray Colors
Enhancements Heat treated (common), fracture-filled (occasional), lattice diffusion.
Typical Treatments Fracture/Cavity Filling, Heat Treatment, Infusion/Impregnation, Lattice Diffusion
Special Care Instructions None
Transparency Transparent to opaque
Absorption Spectrum A distinctive spectrum; a strong red doublet at 6942/6928 is notable, and this may reverse and become fluorescent. Weaker lines at 6680 and 6592. Broad absorption of yellow, green, and violet. Additional lines seen at 4765. 4750, and, 4685. (The reversible fluorescent doublet is a sensitive test for the presence of chromium in a corundum. Even mauve and purple sapphires have a trace of Cr and show these lines).
Phenomena Asterism
Birthstone July
Formula Al2O3 + Cr
Pleochroism Strong: purplish red/orangey red.  (Trace minerals can dampen this effect).
Optics RI: o = 1.757-1.770; e = 1.765-1.779 (usually 1.760, 1.768); Uniaxial (-)
Optic Sign Uniaxial -
Etymology From the Latin ruber for red.
Occurrence Metamorphosed crystalline limestones and dolomites, as well as other metamorphic rock types such as gneiss and schist. Also, igneous rocks such as granite and nepheline syenite.
Inclusions Natural rubies: silk, rutile needles, usually crossing at a 60 degree angle. Zircon crystals with halo of dark fractures, fingerprints, hexagonal growth lines, color zoning. Synthetic rubies: see "Synthetics" below.

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