Gemology (from the Latin “gemma” – jewels and “logos” – science) means the science of jewelry minerals (gemstones). It is an interdisciplinary science that covers not only gems testing, grading, cutting, and pricing but all steps in the entire process of their production to turn them into samples of jeweler’s art, including detection of laboratory-grown samples, treatments, and simulants.
Basic terms in Gemology:
- Natural minerals – they are formed in nature. According to the classification of Kievlenko 1973 (with additions in 1983), natural minerals are of three types:
Jewelry minerals are used for making jewelry and possess beauty (defined by color, luster, transparency, optical effects), rarity, and durability. This group includes diamond, ruby, emerald, sapphire, alexandrite, aquamarine, spinel, demantoid, rhodolite, pyrope, almandine, topaz, tourmaline, chrysolite, zircon, iolite, amethyst, citrine, etc.
Jewelry-decorative minerals are transparent to translucent with lower Mohs hardness such as malachite, nephrite, jadeite, lapis lazuli, rhodonite, amazonite, hematite, feldspar, etc. They are used both in jewelry and for decoration.
Decorative are all colored minerals and rocks (marble, serpentine, jasper, etc.) used for decoration, mosaics, small figurines, and household objects. They are opaque but possess beautiful color patterns or optical effects.
- Synthetic analogs are laboratory-grown with the same chemical composition, crystal structure, color, and properties as natural minerals. The only difference between natural and synthetic analogs (natural and synthetic diamond, natural and synthetic ruby, etc.) is the type of their inclusions.
- Synthetics without natural analogs are laboratory-grown without natural analogs in chemical composition such as YAG, GGG, cubic zirconia, etc. They possess beauty, transparency, and durability.
- Simulants are materials such as glass, plastic, enamel (hot and cold enamels), resins, etc., which mimic one or more properties of a natural mineral, but all other properties differ from it.
- Composite materials or so-called grafted stones consist of two (doublets) or three (triplets) glued parts. For example, the crown is a colorless low-value sapphire glued to a blue glass pavilion, or the crown and pavilion are colorless sapphires with red glass in the middle. The purpose is to strengthen some natural minerals (such as opal) or mislead the buyer about a falsely expensive crystal.
- Treated stones are natural or synthetic minerals processed to improve their quality. Used methods are coloring, irradiation, thermal and chemical processing. Often changes in the physical characteristics of the stone (e. g. color, clarity) are accompanied by changes in the crystal lattice.
- Reconstructed minerals are products formed by joining (pressing, sintering) small pieces of natural minerals into one (e. g. amber).
- Organic gemological materials are formed as a result of vital activity of different organisms or are parts of them: pearl, coral, amber, bone (elephant, mammoth, walrus, rhino, narwhal), bumper from turtle, etc.
- Collectible samples are close to ideal morphology, rare and beautiful color patterns, or optical effects.
Gemological methods for investigation are non-destructive and therefore suitable for archaeological artifacts study.
Gemstones and materials