Precious Stones
A gemstone, gem or also called precious or semi-precious stone is a extremely striking and valuable piece of mineral, which — when cut and polished — is used in jewelry or other decorations. Though certain rocks and organic materials are sternly speaking not minerals, but are still applied in jewelry and decorations, and are thus often considered a gemstone as well. A few minerals that are too soft to be normally applied in jewelry may still be considered a gemstone since of their amazing color, lustre or other physical assets that have aesthetic value. Rarity is another feature that lends value to a gemstone.
Distinctiveness and classification:
Gemstones are portrayed by gemologists using technical specifications. Initial, what is it made of, or its chemical composition? Gems are classified into diverse groups, species, and range. Gems have refractive index, dispersal, specific gravity, rigidity, cleavage, fracture, and lustre. They may display pleochroism or twofold refraction. They may have luminescence and a characteristic absorption spectrum.
Worth of Gemstones, Past and Present:
The diamond is a gemstone which has its value found in a diverse way than most or even all other gemstones. Conventionally the diamond was valued mostly for its physical properties such as rigidity and brilliance, not unlike any other gemstone.
General physical distinctiveness that make a colored stone valuable are color, clarity to a smaller extent cut, odd optical phenomena within the stone such as color zoning, and asteria. The Greeks for instance to a great extent valued asteria in gemstones, which were regarded as a influential love charm, and Hellen of Troy was known to have worn star-corundum.
In history gemstones were classified into precious stones and semi-precious stones. As such a definition can change over time, differ per culture and can depend on so many issues, it has always been a hard matter to ascertain what constitutes precious stones.
Grading:
In the last two decades there has been a propagation of certification, not only for diamonds but for gemstones as well. There are five main laboratories which grade and give reports on gemstones.
- Gemological Institute of America (GIA)
- American Gemological Society (AGS) is not as widely recognized nor as old as the GIA but garners a high reputation.
- American Gem Trade Laboratory which is part of the American Gem Trade Association (AGTA) the largest trade organization of jewelers and dealers of colored stones
- American Gemological Laboratories (AGL) which was recently taken over by "Collector's Universe" a NASDAQ listed company which specializes in certification of many collectables such as coins and stamps
- European Gemological Laboratory (EGL).
Cutting and polishing:
The two chief classifications are stones cut as smooth, dome shaped stones called cabochons, and stones which are cut with a faceting machine by polishing small flat windows called facets at ordinary intervals at intended angles.
Stones which are thick such as opal, turquoise, variscite, etc. are normally cut as cabochons. These gems are designed to illustrate the stone's color or surface properties as in opal and star sapphires. Grinding wheels and polishing particulars are used to grind, shape and polish the smooth dome shape of the stones.
Gems which are transparent are usually faceted; a method which shows the optical properties of the stone’s interior to its best benefit by increasing reflected light which is perceived by the viewer as sparkle. The facets must be cut at the proper angles, which differ depending on the optical properties of the gem. If the angles are too sheer or too shallow, the light will pass all the way through and not be reflected back toward the viewer. Particular equipment, a faceting machine, is used to hold the stone onto a flat lap for cutting and polishing the plane facets. Hardly ever, some cutters use particular curved laps to cut and polish curved facets.
Gemstone color:
Color is the most clear and striking feature of gemstones. The color of any material is due to the nature of light itself. The dissimilarity in color is based on the atomic structure of the stone. Though the dissimilar stones formally have the same chemical composition, they are not precisely the same. Every now and then an atom is replaced by a wholly diverse atom. These so called impurities are enough to absorb certain colors and leave the additional colors unaffected.
Treatments Applied To Gemstones:
Gemstones are frequently treated to enhance the color or clarity of the stone. Depending on the kind and extent of treatment, they can affect the value of the stone. A few treatments are used widely and accepted in practice as the resulting gem is stable, while others are not accepted most frequently since the gem color is unstable and may relapse to the original tone.
Heat
Radiation
Waxing/oiling
Fracture Filling
Synthetic and artificial gemstones:
A few gemstones are manufactured to copy other gemstones. For instance, cubic zirconia is a synthetic diamond simulant composed of zirconium oxide. The reproduction copy the look and color of the real stone but own neither their chemical nor physical uniqueness. On the other hand, true synthetic gemstones are not necessarily imitation. For instance, diamonds, ruby, sapphires and emeralds have been manufactured in labs, which possess very nearly the same chemical and physical distinctiveness to the naturally occurring range. Synthetic corundums, counting ruby and sapphire, are very frequent and they cost only a fraction of the natural stones. Slighter synthetic diamonds have been manufactured in bigger quantities as industrial abrasives for several years. Only lately, larger synthetic diamonds of gemstone quality, particularly of the colored variety, have been manufactured.
Precious Stones