Handbook

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Gemology (from the Latin “gemma” – jewels  and “logos” – science) literally means the science of gemstones. It is an interdisciplinary science that covers not only the study of properties and grading of gemstones, but the entire process of their production to turn them into samples of jeweler’s art, including methods for synthesis, treatment and others.

 

Basic terms in Gemology:

  1. Natural minerals – they are formed in nature without human interference. According to the classification of Kievlenko 1973 (with additions in 1983) natural minerals are divided into:

Jewelery minerals – they are used in jewelery industry for making jewelry and possess the following qualities: beauty (determined 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 – this group combines transparent to translucent minerals with relative lower hardness: malachite, nephrite, jadeite, lapis lazuli, rhodonite, amazonite, hematite, feldspar and so on. They are used both in jewelry, and for decoration.

Decorative minerals – these are all colored minerals and rocks (marble, serpentine, jasper, writing granite, etc.) which are used for decoration, making mosaics, small figurines, household objects and more. They are mostly opaque, but have interesting color or optical effects.

  1. Synthetic analogues – synthesized in the laboratory and have the same chemical composition and crystal structure as certain natural minerals, similar to their color, the same or similar optical and physical characteristics. They differ from their natural analogues only in inclusions – examples: natural and synthetic diamond, natural and synthetic ruby and so on.
  2. Artificial material – synthesized in the laboratory and have no natural analogue in chemical composition. Possess beauty, transparency and durability – YAG, GGG, cubic zirconia and others.
  3. Imitations – these are mostly man-made 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.
  4. Composite materials or so called grafted stones. They can be made of two glued parts – doublets (e.g. crown is colorless sapphire low value and pavilion is blue glass) or three parts – triplets (e.g. crown and pavilion are colorless sapphire and between them – red glass). They are made to strengthen some natural minerals (e.g. opal) or to deceive the buyer that buys an expensive crystal.
  5. Treated stones – natural minerals that have undergone a process improving their quality – coloring, irradiation, thermal and chemical processing. Changes in the physical characteristics of the stone (e.g. color, clarity) may be accompanied by changes in the crystal lattice.
  6. Reconstructed minerals – products formed as a result of joining (pressing, sintering) small pieces of natural minerals into one (e.g. amber).
  7. Organic gemological materials – 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 and others.
  8. Collectible sample– characterized with preserved form (close to perfect) or rare color, pattern and more.

Gemological methods for gemstone identification and grading are non-destructive and therefore they are also suitable for studying archaeological artifacts.

 Gemstones and materials