Gemstone

Gemstone:

Gemstone, also called as jewel, precious stone, fine gem or semiprecious stone is a piece of mineral crystal which is used to make jewelry or other adornments in cut and polished form. However, certain rocks such as lapis lazuli and opal are also considered as gemstones and are used for jewelry. Organic materials that are not minerals such as amber, jet and pearl are also considered to be gemstones as well and are used for jewelry. Gemstone are used as religious symbolism, and because of their healing powers.

Characteristics and classification of Gemstone:

 

• Gemstone can be classified as precious and semi-precious.
• The precious stones are emerald, ruby, sapphire and diamond, and all other gemstones are semi-precious.
• All gemstones are translucent with fine color in their purest forms, except diamond, which is colorless and very hard, with hardness of 8 to 10 on the Mohs scale.
• All other gemstones are classified by their color, translucency, and hardness.
• Gemstones are identified by gemologists, who describe gems and their characteristics such as its chemical composition, using technical terminology. eg. diamonds are made of carbon and rubies are made of aluminium oxide.
• Gems those are crystals can be classified by their crystal system such as cubic or trigonal or monoclinic.
• These can also be classified as habit. It is the form in  which the gem is usually found. eg. diamonds are often found as octahedrons which have a cubic crystal system.
• Gemstones can be classified into different groups, species and varieties. eg. ruby is the red variety of the species corundum, where as any other color of corundum is considered as sapphire.
• The emerald (green), red beryl (red), goshenite (colorless), aquamarine (blue), heliodor (yellow) and morganite (pink), are all varieties of the mineral species beryl.
• Gems are characterized in terms of refractive index, specific gravity, hardness, dispersion, cleavage, fracture and luster.
• They may exhibit pleochroism or double refraction and may have luminescence as well as a distinctive absorption spectrum.
• Gemstones are also be classified in terms of their luster, transparency, or brilliance. Very transparent gems are considered as 'first water', while those with lesser transparency are considered as 'second' or 'third water' gems.

Value of Gemstone:

 

• All gemstones were graded using the naked eye during ancient time. However, a system developed by the Gemological Institute of America (GIA) in the early 1950s included a major innovation by the introduction of 10x magnification as the standard for grading clarity.
• Diamonds are graded using the GIA system while other gemstones are still graded using the naked eye.
• The factors used to grade a diamond can be described by a mnemonic device, the 'four Cs' including color, cut, clarity, and carats.
• These categories can be useful in understanding the grading of all gemstones with modification.
• Color o a gemstone is its physical characteristics that make a colored stone valuable. Clarity to a lesser extent, cut, unusual optical phenomena can also contribute to its value.
• Diamonds, rubies, sapphires, and emeralds are considered as the most valuable gemstone than others.
• Pricing and value of a gemstone are governed by factors and characteristics in the quality of the stone which include clarity, rarity, freedom from defects, the beauty of the stone and the demand for such stones.
• The pricing of colored stones is determined by market supply and demand. However, the value of diamond can change based on location, time, and on the evaluations of diamond vendors.

Cutting and polishing of Gemstone:

 

• Very few gemstones are used as gems in the crystal or other forms in their original form in which they are found. Most of the gemstones are cut and polished for usage as jewelry. 
• Cabochons and Facets are the two main classifications for cutting and polishing of Gemstone. 
• Stones those are cut as smooth, dome-shaped stones are called as cabochons where as stones which are cut with a faceting machine by polishing small flat windows at regular intervals at exact angles are called facets.
• Stones which are opaque or semi-opaque are commonly cut as cabochons. Theses include opal, turquoise, variscite, etc which are designed to show the color or surface properties of the stone.
• The smooth dome shape of the stones are grinded, shaped and polished by using grinding wheels and polishing agents.
• Gems that are transparent are normally faceted, in which the optical properties of the stone's interior can be shown to its best advantage by maximizing reflected light which is perceived by the viewer as sparkle.
• The facets should be cut at the proper angles, which varies depending on the optical properties of the gemstone. The light will pass through and not be reflected back toward the viewer if the angles are too steep or too shallow.
• The stone will be hold onto a flat lap for cutting and polishing the flat facets by using the faceting machine. Special curved laps are rarely used to cut and polish curved facets.

Colors of Gemstone:

 

• The color of any gemstone is due to the nature of light itself. 
• Most of the light is absorbed while a smaller amount of a particular frequency or wavelength is reflected when light strikes a material.
• The perceived color is the part that is reflected and reaches the eye.
• A ruby appears red as it absorbs all the other colors of white light, reflecting the red.
• Same material can exhibit different colors. For example, both ruby and sapphire are corundum having the same primary chemical composition but exhibit different colors because of impurities.
• The same named gemstone can also occur in many different colors. For example, sapphires can be of different shades including blue and pink. 'Fancy sapphires' exhibit a whole range of other colors from yellow to orange-pink.
• This difference in color is due to the atomic structure of the stone.
• Although the different stones have the same chemical composition and structure, they are not exactly the same because of the  impurities in it which are sufficient to absorb certain colors and leave the other colors unaffected.
• For example, beryl is colorless in its pure mineral form, which becomes emerald with chromium impurities. Beryl becomes pink morganite if  manganese is added instead of chromium. It becomes aquamarine with iron.
• The color of the gem can be changed as these impurities can be manipulated by using some gemstone treatments.

Treatment of Gemstone:

The color or clarity of the gemstone can be enhanced by treatment. The value of the stone gets affected depending on the type and extent of treatment.
These treatments are used only if the resulting gem is stable. The gem color is unstable and may revert to the original tone in some cases.

Heat Treatment:

 

• The color or clarity of gemstone can be improved or spoiled by heat.
• Heating amethyst will result in citrine. Ametrine is a stone that partly amethyst and partly citrine, can be formed by partial heating with a strong gradient.
• The yellow tones of Aquamarine can be removed by heating it. Its green colors will be changed into the more desirable blue, or its existing blue color will be enhanced to a deeper blue by heating it.
• Almost all tanzanite is heated at low temperatures to remove brown undertones and give it a more desirable blue or purple color.
• Both color and clarity of a considerable portion of all sapphire and ruby can be improved by treating with a variety of heat treatments.
• The diamond should be protected with boric acid when jewelry containing diamonds is heated for repairs as  the diamond is pure carbon, and could be burned on the surface or even burned completely up.
• Jewelry containing sapphires or rubies do not have to be protected from burning, like a diamond. However, these stones need to be protected from heat stress fracture by immersing the part of the jewelry with stones in the water when metal parts are heated.

Radiation Treatment:

 

• Diamonds are irradiated to produce naturally occurring fancy-color diamonds.
• The lighter and the darker blue shades of topaz such as 'London' blue, are produced by exposing to radiation to change the color from white to blue.
• The yellow-green color of most quartz can be achieved by exposing to radiation.

Waxing/oiling Treatment:

 

• Wax or oil is sometimes filled with Emeralds containing natural fissures to disguise them.
• Emerald can appear better color as well as clarity by using colored wax.

Synthetic and Artificial Gemstones:

 

• Synthetic and artificial gemstones are created in a laboratory which are physically, optically, and chemically identical to the natural stone.
• These are chemically different from the natural stone, but may appear quite similar to it.
• Synthetic gemstones of a different mineral (spinel), glass, plastic, resins, or other compounds can be easily manufactured.
• Cubic zirconia is an example of simulated or imitation stones which is composed of zirconium oxide, synthetic moissanite, and un-colored, synthetic corundum or spinels.
• The simulants looks similar to the real stone but does not possess any chemical or physical characteristics of them.
• Gemstones those are cultured, synthetic, or lab-created are not imitations as the bulk mineral and trace coloring elements are the same in both.
• For example, diamonds, sapphires, rubies and emeralds those are manufactured in labs possess identical chemical and physical characteristics to the naturally occurring variety.
• Synthetic corundum, including ruby and sapphire, which are created in lab are very common and less expensive than the natural stones.
• The chemical, physical, and optical characteristics remains the same in both natural stone or synthetic gemstone as they are composed of the same mineral and are colored by the same trace materials.
• The hardness, density and strength will be same in both the types, and they also show the same color spectrum, refractive index, and birefringence.
• Synthetic stones tend to have a more vivid color as impurities found in natural stones are not present in these stone.
• The gem clarity or color will be reduced in synthetic stones as they are made free of common naturally occurring impurities

Precious Gemstones:

Gems are regarded as miraculous and endowed with mysterious powers in addition to their use as jewelry. Natural minerals including  beryl, chrysoberyl, corundum, diamond, feldspar, garnet, jade, lazurite, olivine, opal, quartz, spinel, topaz, tourmaline, turquoise, and zircon have achieved importance to be used as gemstones. More than one type of gem can be provided by some of these minerals. For example, beryl provides emeralds and aquamarines, while corundum provides rubies and sapphires.
Some of the Precious Gemstones are:

• Tanzanite has a deep blue-violet hue and is found only in northern Tanzania in the Mirerani Hills.
• Opal is dark black in color but also has a surprising array of color. Most black opal gems are found in the Lighting Ridge area of New South Wales, Australia.
• Musgravite is a rare gemstone which is an aluminum oxide stone with iron, zinc, and magnesium. It was discovered in the Musgrave Ranges of Australia. It is available in a wide range of color from translucent olive green to a greyish purple.
• Red beryl is colorless in its pure form, consisting of beryllium, aluminum, and silicate. Typically, Red Beryl gems are small. Gem-quality specimens are only found in Utah's Wah Wah Mountains which are found in shades of dark red. The color of this gem is determined by traces of other elements in the stone.
• Alexandrite is a type of chrysoberyl that includes impurities such as titanium, chromium, and iron. It changes colors depending on the light. It appears emerald in light condition, while it is ruby red in the dark. It is mostly found in Russia, but also mined in India and Sri Lanka.
• Emerald is one of the world's most popular gemstones because of its exotic green tones. Most emeralds have some minor imperfections. Flawless Emerald can hit extraordinarily high values.
• Rubies are known for their vibrant red colors and range from pink to dark red. They symbolize passion and a zest for life.
• Diamonds are composed of pure carbon and is mostly used in engagement and wedding rings. The diamond was thought to give its wearer strength in battle and to protect him against ghosts and magic by many civilizations.  

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