Ruby Properties, Treatments and Value

Natural Rubies

Both ruby and sapphire are from the species corundum and are the hardest known minerals after diamond. Corundums of gemstone quality of all colors except red are called sapphire. Red varieties are called rubies, because of its red color (Latin = ruber).


Color:  Varying red

Moh’s Hardness:  9.0

Chemical Composition:  Aluminum oxide

Where Mined:  Myanmar, Thailand, Sri Lanka, Tanzania, Australia, Brazil

Transparency:  Transparent to opaque

Common Enhancements:  heat treated, flux filling

Color Change: more vivid red

Type of cut:  mixed cut, 

Gemstone of the Month for July

Zodiac gemstone:   Aries (March 21 – April 20)

Current retail Per Carat Price range:  $600 - $10,100 US


The red color varies within each individual deposit, so it is not possible to determine the source area from the color. The designations “Burma or Siam ruby” are erroneous and refer more to quality than origin. The most desirable color is “pigeon’s blood” which is a pure red with a hint of blue. The distribution of color is often uneven, in stripes or spots.

The substance that provides the color is chromium, and in the case of brownish tones, iron is present as well. As a rough stone, it appears dull and greasy, but when cut the luster can approach that of diamond. Heat treatment is commonly used to enhance the color.

Rough raw Ruby before cutting

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Rubies are the most valuable members of the corundum family. Large, gem quality stones can be more valuable than comparably sized diamonds and are certainly rarer. Small gem quality stones are rarer than comparable blue or other color sapphires, making even the littlest fine gemstones relatively high in value. Many gems increase exponentially in value with increase in carat size, and this is particularly true of fine ruby gems.

Stones of Burmese origin generally command the highest prices. Strong color saturation, eye clean or better clarity, and strong fluorescence elevate prices sharply.

Next to diamonds, red rubies are probably the most expensive gemstones in the world in sizes over 3 ct. The ideal color is that of a red traffic signal, a highly fluorescent red of high intensity.

Unlike diamond, small amounts of silk in a stone actually help the color because they scatter light into areas it would not otherwise go. This helps cover up the extinction which would otherwise be found. Thai/Cambodian rubies suffer the double deficiency of too much iron, which cuts the fluorescence, and no silk to scatter light.

This gemstone is the hardest mineral after diamond and moissanite, however the hardness varies in different directions. This gemstone has no cleavage, but has certain preferred directions of parting, Because of brittleness, care must be taken when cutting and setting.

Rubies and sapphires may be faceted in many different styles; mostly the mixed cut is used; the brilliant-cut crown is backed with a step-cut pavilion.

For fine stones the step cut is often employed, and if the material is poor quality or much flawed it may be cut into beads or even carved. Pale stones are often mounted with a closed setting and the back of the stone is sometimes foiled with a suitable color.

Common treatments or enhancements for ruby = heat treated, flux filling 

Heat Treated Ruby - Before and After

Criteria for Assessing a Ruby's Grading:

Flowchart for assessing the grading of a Ruby
Ruby Grading System

Current Retail Ruby Value and Per Carat Prices:

Historical average values for Ruby, courtesy of gemval.com
Relative index, Jul 2005 = 100.00

Historical Average Values for Ruby (2005 - 2014)

Current Per Carat retail Price range for Ruby =

 $600 - $10,100 US



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