WHAT IS A GEM ? A gem is a mineral cut and polished for ornamental use. Gemstones are minerals, the fundamental building blocks of the earth. A mineral is a naturally occurring inorganic chemical element or compound, with definite crystal structure and a composition that varies within defined limits.
Not all minerals are useful as gems. Since gems must be visually attractive, only minerals with ornamental qualities are suitable. This criterion reduces the total of about 2400 known mineral species to approximately 100 that have been cut into gemstones.
Some minerals of biological origin (organic) are also used as gems. These include amber, coral, pearl, shells, ivory and jet, a hard variety of coal. Organic gems lack the durability and hardness of many minerals, but have been highly valued because of their beauty and scarcity.
In the past the terms “precious” and “semi-precious” have been extensively used. These terms are used even today by the public and jewelry traders alike. The dictionary defines precious as “of great value or high price”; and semi-precious as “of less commercial value than precious”. In the past, the so-called precious stones were diamond, ruby, emerald, sapphire, pearl, and occasionally opal. Apart from that, all the other gems fell under the semi-precious category. This indicates clearly that this nomenclature is a marketing term, primarily based on value of gemstones. However it is worth noting that a poor diamond can be worth less than a very fine and rare variety of garnet; which has always been regarded as semi-precious.
A material, to be considered a gem, must have above all, properties pertaining to beauty, durability, and scarcity. Portability can also be a factor in some cases.
1) Hardness is a major factor. If a gem is too soft it will scratch easily, and if worn, its beauty would be rapidly lost due to abrasion. Some extremely soft minerals are cut for collectors and can be thought of as non-commercial gems. But their lack of durability makes it questionable if the term “gem” can be applied to them. Durability combines various characteristics into a general term that indicates how well a gem wears in daily use. Objects such as pearls are not too hard, but hold up well and retain their beauty for a long time and is used extensively in jewelry.
2) Rarity or Scarcity is another major factor in evaluating a gem, for much of a gem’s value comes from its scarcity. The material itself might be very uncommon. On the other hand, the rarity of a particular gem might be due to its large size compared to most other gems of the same material, or its extremely fine or unusual color.
3) Beauty is the most important criterion of all. It depends, of course, on the judgment of the observer and is thus almost totally subjective. But more significant is the fact that what is generally considered beautiful or desirable may change with time, and vary from one culture to another. The value of gems is thus intimately linked to fashion, and the vogue of the time. Transparency, clarity, color and optical properties and phenomenon in gemstones add to its beauty.
Transparency is the absence of “cloudiness” or “milkiness” that would scatter light entering a gem. Clarity, or freedom from flaws, largely determines value in the case of faceted gems. Since most minerals acquire internal imperfections or flaws as a normal part of the growth process, completely flawless or “clean” gems are extremely scarce in many mineral species. For example, in Colombian emerald and Burmese ruby such perfection is almost unknown. Even nearly flawless gems of such materials are in great demand and command a high price. In the case of quartz and topaz, on the other hand, large transparent and clean gems are frequently cut.
Color is of supreme importance in a gem. It can make the difference between NRs 1,000 and 100,000 per carat in some gemstones. The range of color to be found in the mineral kingdom is enormous, and there is great delicacy in the variation of color in a single mineral species. Some minerals occur in a wide range of colors, such as tourmaline, beryl, quartz, and spinel. In this case value is directly linked to the fashion of the times, meaning what color is considered “most desirable”.
Brilliance and dispersion affect gem value, especially in the case of colorless materials. Brilliance is the effect produced by the return of light from the gem to the eye, and is largely a function of proper cutting. Dispersion is the optical phenomenon that creates the color play in diamond.
4) Portability is a less obvious but very important aspect of gem value. Diamonds worth several million rupees can be easily carried in a purse or pocket. Only gemstones can offer this degree of high value in a small space.