Ruby

Click here to view all significant Ruby gemstones

Significant stones

Name	Weight	Country of Origin	Current Owner
Eminent Star	6,465.00 cts	India
Ecce Homo Star Ruby	2,890.00 cts	Mozambique
Edwardes Ruby	167.00 cts
Rosser Reeves Star Ruby	138.70 cts	Sri Lanka
Anne of Brittany's	105.00 cts
DeLong Star Ruby	100.32 cts	Myanmar	American Museum of Natural History
De Long Star Ruby	100.32 cts	Myanmar
Edith Haggin de Long Star Ruby	100.32 cts	Myanmar

Ruby Treatments

Heat-treatment may create a superficial chalky-blue reaction. May be dyed (especially cabochons): color concentration in cracks. Acetone test.
Diffusion: may show orangy color concentration/rim under surface. May show blue haloes/spots (internal diffusion). May be surface diffused (chromium): rare. Glass filling: rounded and flattened gas bubbles, glassy residues. Reflecting light: filled cracks may show a distinct surface lustre. Lead-glass (and some other high refractive glasses) may be revealed by bluish to orangy flashes seen when looking parallel to filled cracks, using dark-field or fiber-optic light. Some glass-filled rubies may not show colored flashes nor show obvious gas bubbles. Sensitive to solvents - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p. 2
Lattice diffusion with beryllium enhances the colour giving orangy-red or red face-up colour. Fracture-filling with high-lead-content glass.Exposure to chemicals (even some household cleaners) can damage the filler material and make fracture more visible. - GIA, 2018

Ruby Simulants

Imitation rubies are also marketed. Red spinels, red garnets, and colored glass have been falsely claimed to be rubies. Imitations go back to Roman times and already in the 17th century techniques were developed to color foil red—by burning scarlet wool in the bottom part of the furnace—which was then placed under the imitation stone.

Synthetic Ruby

In 1837 Gaudin made the first synthetic rubies by fusing potash alum at a high temperature with a little chromium as a pigment. In 1847 Ebelmen made white sapphire by fusing alumina in boric acid. In 1877 Frenic and Freil made crystal corundum from which small stones could be cut. Frimy and Auguste Verneuil manufactured artificial ruby by fusing BaF2 and Al2O3 with a little Chromium at red heat. In 1903 Verneuil announced he could produce synthetic rubies on a commercial scale using this flame fusion process. By 1910, Verneuil's laboratory had expanded into a 30 furnace production facility, with annual gemstone production having reached 1,000 kg (2,205 lb) in 1907.

Other processes in which synthetic rubies can be produced are through the Czochralski's Pulling process, flux process, and the hydrothermal process. Most synthetic rubies originate from flame fusion, due to the low costs involved. Synthetic rubies may have no imperfections visible to the naked eye but magnification may reveal curves, striae and gas bubbles. The fewer the number and the less obvious the imperfections, the more valuable the ruby is; unless there are no imperfections (i.e., a "perfect" ruby), in which case it will be suspected of being artificial. Dopants are added to some manufactured rubies so they can be identified as synthetic, but most need gemological testing to determine their origin.
Synthetic rubies are used for watches and bearings, formerly the most important technical application for natural stones. - Gemstones of the world, Walter Schumann, 2001, p 82

Physical Properties of Ruby

Mohs Hardness

Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)

Specific Gravity

3.97 to 4.05

Tenacity

Brittle

Cleavage Quality

None

Fracture

Conchoidal,Splintery

Walter Schumann, Gemstones of the world (2001) Small conchoidalMore from other references

Optical Properties of Ruby

Refractive Index

1.762 to 1.778

Optical Character

Uniaxial/-

Birefringence

0.008

Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)

Pleochroism

Strong: purplish-red - orangy-red

Dispersion

0.018

Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)

Chatoyancy

Star 6

Colour

Colour (General)

Near colourless through pink through all shades of red to a deep crimson.

Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)

Colour (Chelsea Filter)

Fluorescent red

Causes of Colour

Red, Cr³⁺ in octahedral coordination with minor contributions of V³⁺ and Fe³⁺ in octahedral coordination.

W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)

Transparency

Transparent,Translucent,Opaque

Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)

Lustre

Subadamantine,Vitreous,Pearly

Michael O’Donoghue, Gems, Sixth Edition (2006) Pearly on parting surfaces

Fluorescence & other light emissions

Fluorescence (Short Wave UV)

Inert to (strong) red

Fluorescence (Long-Wave UV)

Moderate to strong red. A red-inhibiting filter may reveal an orange fluorescence.

Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)

Crystallography of Ruby

Crystal System

Trigonal

Habit

Hexagonal prisms or tables, rhombohedrons

Geological Environment

Where found:

The host rocks of ruby are metamorphic dolomite marbles, gneiss and amphibolite. The yield of rubies from such primary deposits is not economically profitable. Rather secondary alluvial deposits are worked. Because of its high density, ruby is normally separated through the washing of river gravels, sands, and soil, then concentrated, and finally picked out by hand.