Definition and Classification of Gemstones
- Gemstones are mineral crystals used for making jewelry and adornments.
- They can be precious or semi-precious stones.
- Some rocks and organic materials are also considered gemstones.
- Gemstones are valued for their hardness, luster, and rarity.
- Gemstones are classified as precious or semi-precious based on rarity and quality.
- The traditional precious stones are emerald, ruby, sapphire, and diamond.
- Other gemstones are classified by color, translucency, and hardness.
- The terms precious and semi-precious can be misleading in a commercial context.
- Gemstones are identified by their chemical composition, crystal system, and habit.
- Gemstones belong to different species and varieties.
- For example, ruby is the red variety of the species corundum.
- Gemstones are characterized by refractive index, dispersion, hardness, and luster.
- They may exhibit pleochroism, double refraction, and luminescence.
- Inclusions and flaws may be present within gemstones.
- Gemstones do not have a universally accepted grading system.
- Diamonds are graded using a system developed by the Gemological Institute of America.
- The four Cs (color, cut, clarity, and carats) are used to grade diamonds.
- The cut is the primary determinant of value in diamonds.
- The purity and beauty of color are important for colored gemstones.
- The pearl and opal have been considered precious alongside diamond, ruby, sapphire, and emerald.
- Aquamarine, peridot, and cat's eye have also been regarded as precious in the past.
- The distinction between precious and semi-precious gemstones is no longer made in the gemstone trade.
- Gemstone pricing is influenced by factors such as clarity, rarity, and demand.
- Diamonds, rubies, sapphires, and emeralds still have a reputation that exceeds other gemstones.
Gemstone Grading and Evaluation
- Gemological Institute of America (GIA) is the main provider of education services and diamond grading reports.
- International Gemological Institute (IGI) is an independent laboratory for grading and evaluation of diamonds, jewelry, and colored stones.
- Hoge Raad Voor Diamant (HRD Antwerp) is one of Europe's oldest laboratories, with its main stakeholder being the Antwerp World Diamond Centre.
- American Gemological Society (AGS) is a recognized laboratory, although not as widely known as GIA.
- American Gem Trade Laboratory is part of the American Gem Trade Association (AGTA) and focuses on colored stones.
Gemstone Cutting and Polishing
- Gemstones are commonly cut and polished for use in jewelry.
- Cabochons are smooth, dome-shaped stones, while faceted stones have small flat windows called facets.
- Opaque or semi-opaque gems like opal and turquoise are often cut as cabochons.
- Transparent gems are faceted to maximize reflected light and sparkle.
- Different angles must be cut for the facets to ensure proper reflection.
Gemstone Colors and Treatment
- The color of a gemstone is determined by the nature of light and the wavelengths that are reflected.
- Impurities in gemstones can cause variations in color.
- Even gemstones with the same chemical composition can exhibit different colors due to impurities.
- Beryl, for example, can become emerald with chromium impurities or pink morganite with manganese impurities.
- Gemstone treatments are often used to enhance their color, clarity, and durability.
- Some treatments can affect the value of the stone.
- Heating is a common practice in the gemstone industry.
- Radiation treatment enables the creation of rare gemstone colors.
- Waxing/oiling treatment is used to enhance the color and clarity of gemstones.
- Fracture filling treatment is used to improve the appearance of gemstones with fractures.
- Bleaching treatment is used to alter the color of gemstones.
- Gemstone treatments can be followed by dying or impregnation.
- Synthetic gemstones are created in a laboratory and have the same characteristics as natural stones.
- Imitation or simulated stones are chemically different but may look similar to natural stones.
Synthetic Gemstone Production Methods and Characteristics
- Synthetic gemstones share chemical and physical properties with natural gemstones.
- Microscopy is often used to distinguish slight differences between synthetic and real gemstones.
- Flame fusion, Czochralski, flux growth, and hydrothermal growth are common methods for producing synthetic gemstones.
- Synthetic gemstones have characteristic features specific to the growth process.
- Auguste Verneuil developed the flame-fusion process in 1902.
- Synthetic gemstone production has a long history of innovation and development.
Gemstone Data Sources