Gemstones - Just Minerals Found In Earth?

Since gemstones, with a few notable exceptions, are minerals found in the earth's crust, the laws and procedures applied to the study of minerals fit them perfectly. Any trained mineralogist can soon become a competent gemologist, since he is already familiar with the techniques of identification and knows the fundamental chemistry and physics of natural substances. A mineral is a natural substance having a definite chemical composition and definite physical characteristics by which it can be recognized and distinguished from other substances. Technically, in mineralogy, those natural substances formed by living organisms are excluded. This means that amber and jet, formed by plants, and coral and pearl, produced by animals, are not minerals. However, all four are traditionally included among the gemstones, because they qualify on grounds of beauty, rarity, etc.
The gem mineral's characteristics of brilliance, beauty, and durability arise directly from the kind of chemical composition and also from the kind of internal atomic structure it has. Sometimes, natural accidents of growth and the introduction of impurities during the formation of the gem minerals may enhance their interest and value. On the other hand, severe accidents of growth may destroy their usefulness. Obviously, some understanding of the chemical and physical reasons for mineral characteristics is needed to appreciate and understand gemstones.
Chemical Composition: We know that the universe is made up of a relatively few basic building materials, the hundred-odd chemical elements. Some of their names—gold, silver, copper, sulfur, and oxygen—are very familiar. Popular are especially gold diamond engagement rings Others such as beryllium, zirconium, and boron sound less familiar but are important among gem minerals. Still others are so rare as to be of no importance or interest in this discussion. A small number, perhaps twenty-five, supply materials to make up all significant gemstones. A few more, present in tiny trace amounts, may impart color or other occasional special characteristics.
The elements which go into making up a mineral exist as innumerable, extremely small bodies called atoms. Each kind of atom— e.g., silicon or oxygen—has its own characteristic size and its own particular ability to join with other atoms. In nature, under various temperatures and pressures and in different mixtures, the elements are brought together and combine with each other to form minerals. Since 46y2 percent of the earth's crust is oxygen and 27i/2 percent is silicon, it is not surprising that most minerals contain these two elements.