For centuries, human beings have prized rubies as valuable gems. The brilliant deep red hues of rubies rendered them attractive as jewelry items since ancient times.
But the chemical composition of these precious stones might surprise you, however; they are a crystalline form of aluminum oxide known as the mineral "corundum". (See p. 102 of G. Brocardo's Nature Trek Guide "Minerals & Gemstones of the World" rev. English edition by David&Charles, 1994).
An overview of corundum and rubies
Second only to diamonds on the Mohs scale of hardness, corundum appears around the world in many forms. The Nature Trek Guide indicates that when shaded red, it forms rubies; when blue, sapphires; when purple or violet, amethysts; when green, emeralds; and when yellow, some forms of topaz.
Rubies usually obtain their special firey hue through the addition of small traces of chromium in the corundum. In their natural form, rubies often possess widely varying trace quantities of this element, and sometimes titanium: so their colors may range considerably from lighter to darker shades. Frequently, rubies appear as inclusions within others minerals. They evidently form within the magma of the earth, and often appear surrounded by other types of igneous material. However, the exact process by which natural rubies are created remains a source of debate.
Although extremely brilliant rubies remain highly valuable gems, corundum itself is not a rare mineral. Geologists classify it as common.
One especially important chemical property of rubies is hardness
The hardness of corundum makes the chemical composition of rubies highly useful in many contexts. Jewellers and gem collectors esteem rubies for their natural beauty; when cut and polished, the sharp, clear facets of the stone can appear brilliant. Faceted rubies for generations have appealed to people as valuable gems.
But this same hardness also causes rubies to hold importance in many industrial settings as well. Just like diamonds, rubies can functions sometimes as drilling bits. Some companies use them in lasers, for instance.
Gem collectors grade naturally obtained rubies. Those with the most potential as precious stones often wind up in jewerly items but even the less attractive pieces may find utility in a range of mundane manufacturing or industrial contexts.
Perhaps due to the commercial importance of corundum, scientists as early as the nineteenth century sought ways to produce synthetic rubies. Today, synthetic rubies figure largely in many industrial, business and scientific capacities.
The crystalline lattice of rubies
Corundum consists of a crystalline form of aluminum oxide; unlike diamonds, which gain stregth through their cubic structure, it maintains a natually trigonally shaped crystalline form (See the written guide cited previously) in terms of the lattices of the mineral.
The important properties of rubies in terms of their crystalline lattice shape have evidently contributed to their appeal as gems for centuries. Rubies may be cut and shaped in angles to catch and reflect the light, and even in their natural form, some rubies appear quite brilliant.
This property in the past caused some observers to associate them with mystical qualities. They have been considered gems in many locations around the world as a result.
The chemical composition of rubies allow these gems to function in many capacities. A lovely mineral, the ruby truly deserves its reputation as a precious gem.