Introduction

Ruby is the red variety of the mineral corundum, one of the hardest minerals on Earth, of which the sapphire is also a variety. Pure corundum is colourless. Slight traces of elements such as chrome, iron, titanium or vanadium are responsible for the colour. These gemstones have excellent hardness. On the Mohs scale their score of 9 is second only to that of the diamond. Only red corundum is entitled to be called ruby, all other colors being classified as sapphires. The close relationship between the ruby and the sapphire has only been known since the beginning of the 19th century.

Up to that time, red garnets or spinels were also thought to be rubies. (That, indeed, is why the 'Black Ruby' and the 'Timur Ruby', two of the British Crown Jewels, were so named, when they are not actually rubies at all, but spinels.)

Ruby, this magnificent red variety from the multi-colored corundum family, consists of aluminium oxide and chrome as well as very fine traces of other elements - depending on which deposit it was from. In really fine colors and good clarity, however, this gemstone occurs only very rarely in the world's mines. Somewhat paradoxically, it is actually the coloring element chrome which is responsible for this scarcity. True enough, millions of years ago, when the gemstones were being created deep inside the core of the Earth, chrome was the element which gave the ruby its wonderful color.

But at the same time it was also responsible for causing a multitude of fissures and cracks inside the crystals. Thus only very few ruby crystals were given the good conditions in which they could grow undisturbed to considerable sizes and crystallise to form perfect gemstones. For this reason, rubies of more than 3 carats in size are very rare. So it is no wonder that rubies with hardly any inclusions are so valuable that in good colours and larger sizes they achieve top prices at auctions, surpassing even those paid for diamonds in the same category.

Some rubies display a wonderful silky shine, the so-called 'silk' of the ruby. This phenomenon is caused by very fine needles of rutile. And now and then one of the rare star rubies is found. Here too, the mineral rutile is involved: having formed a star-shaped deposit within the ruby, it causes a captivating light effect known by the experts as asterism. If rubies of this kind are cut as half-dome shaped cabochons, the result is a six-spoked star which seems to glide magically across the surface of the stone when the latter is moved. Star rubies are precious rarities.

Their value depends on the beauty and attractiveness of the colour and, though only to a lesser extent, on their transparency. Fine star rubies, however, should always display rays which are fully formed all the way to the imaginary horizontal line which runs through the middle of the stone, and the star itself should be situated right in the centre.

Rubies can command the highest per-carat price of any colored stone. This makes ruby one of the most important gems in the colored stone market. In its purest form, the mineral corundum is colorless. Trace elements that become part of the mineral’s crystal structure cause variations in its color. Chromium is the trace element that causes ruby’s red color.

Ruby is one variety of the corundum mineral species, which also includes sapphire. Ruby is highly regarded and can command high per-carat prices. It is arguably one of the most important gems in the colored stone market.

Description

In its purest form, the mineral corundum is colorless. Trace elements that become part of the mineral’s crystal structure cause variations in its color. Chromium is the trace element that causes ruby’s red, which ranges from an orangy red to a purplish red.

The strength of ruby’s red depends on how much chromium is present—the more chromium, the stronger the red color. Chromium can also cause fluorescence, which adds to the intensity of the red color.

The most renowned rubies, like those from Myanmar, the Himalayas, and northern Vietnam, typically form in marble. They’re found in layers that are distributed irregularly within the surrounding marble. Marble forms as part of the metamorphic (rock-altering) process, when heat and pressure from mountain formation act on existing limestone deposits.

Product Information

Marble has low iron content, so the rubies that originate in marble (called “marble-hosted” by gemologists) lack iron. Because of this, many have an intense red color.

Facts

• Mineral: Corundum
  
• Chemical composition: Al₂O₃
  
• Color: Red
  
• Refractive index: 1.762 to 1.770
  
• Birefringence: 0.008 to 0.010
  
• Specific gravity: 4.00 (+/- 0.05)
  
• Mohs Hardness: 9

In addition, rubies found in marble typically fluoresce red under ultraviolet light—even the ultraviolet light in sunlight. Fluorescence can make a ruby’s color even more intense and increase its value.
In other locations, rubies can be found in basalt rocks. Rubies from these sources can have higher iron content, which can make the rubies darker and less intense in color. Higher iron content in the chemical makeup of a ruby can also mask the red fluorescence, eliminating that extra glow of red color seen in marble-hosted rubies. Marble has low iron content, so the rubies that originate in marble (called “marble-hosted” by gemologists) lack iron. Because of this, many have an intense red color.

In addition, rubies found in marble typically fluoresce red under ultraviolet light—even the ultraviolet light in sunlight. Fluorescence can make a ruby’s color even more intense and increase its value.
In other locations, rubies can be found in basalt rocks. Rubies from these sources can have higher iron content, which can make the rubies darker and less intense in color. Higher iron content in the chemical makeup of a ruby can also mask the red fluorescence, eliminating that extra glow of red color seen in marble-hosted rubies.

Ruby Birthstone Meaning & History

In ancient India, ruby was called the “king of precious stones” for its rarity, hardness (second only to diamond), beauty and seemingly mystical powers. Long associated with the life force blood, ruby was a symbol of power and youthful energy in Indian jewelry. In past centuries, some believed this birthstone for July could predict misfortune or danger, and others claimed it would cure inflammatory diseases and soothe anger. Burmese warriors believed it made them invincible in battle. Medieval Europeans maintained that rubies bestowed health, wisdom, wealth and success in love.

Where are Rubies Found?

Our search for the July birthstone starts in Myanmar (formerly known as Burma), one of the oldest recorded sources of fine rubies. For more than five centuries, the Mogok area in Myanmar has produced some of the most sought-after rubies – vibrant red beauties softened by light-scattering inclusions and a glowing red fluorescence. The region is a place of weathered marble and ancient Buddhist temples.

Since the late 20^th century, Vietnam has been another important source for the July birthstone. The Luc Yen region in northern Vietnam, where rainforest-clad mountains rise over broad paddy fields, produces rubies of red to purplish red color. Farther south, the Quy Chau district has also yielded many fine rubies. Today, artisanal miners work the soil in hopes of finding a gem that will change their fortunes.

Mozambique is an important new source for the July birthstone. This African nation is home to the prolific mines at Montepuez. Rubies found there have been compared to the famed gems of Mogok.

For many years in the late 1900s, the ruby deposits along the border between Thailand and Cambodia were the major source of rubies in the marketplace. Other important producers of the July birthstone include Afghanistan, Tajikistan, Pakistan, Sri Lanka, Kenya, Tanzania and Madagascar.