Читать книгу Geology and Mineralogy of Gemstones - Karl Wallace, David Turner R. - Страница 22

Elements combine and interact through chemical bonds. When two or more elements join together they form a compound. As with an element, a compound is represented by symbols called chemical formula. Examples of common compounds and their formulae are water (H₂O), composed of hydrogen (H) and oxygen (O), and common table salt, (NaCl) composed of sodium (Na) and chlorine (Cl). Most gemstones are compounds, such as sapphire (Al₂O₃), composed of aluminum (Al) and oxygen, and emerald (Be₃Al₂Si₆O₁₈), composed of beryllium (Be), aluminum, silicon (Si), and oxygen.

Mixtures differ from compounds in that a mixture is comprised of two or more compounds that are not interacting through chemical bonding. The world of rocks and minerals is a perfect example of this. Minerals, like sapphires, are compounds that are held together through chemical bonding. Rocks, on the other hand, can be thought of as bulk mixtures of minerals held together through an interlocking physical network of mineral grains not through chemical bonding. This is similar to how furniture can be made whole with joints, nails, and screws that physically hold the pieces together while the individual pieces are independently held together through chemical bonding that make up the wood itself.