While considering the gem, the properties of the stone can vary tremendously. This is because unlike other groups of objects, such as wood, metals, even minerals, the requirements for something being a gem stone are very arbitrary. The study of gem stones properties is very important to both the gem cutter and setter as well as to the consumer who can use that information to care for the While considering the gem, the properties of the stone can vary tremendously. This is because unlike other groups of objects, such as wood, metals, even minerals, the requirements for something being a gem stone are very arbitrary. The study of gem stones properties is very important to both the gem cutter and setter as well as to the consumer who can use that information to care for the gem. Gemstone properties can be divided into two categories: Physical: The physical properties of gemstones, their hardness, their specific gravity or density and the way they break, depend on chemical bonding and the atomic structure within the stone. 1. Specific Gravity: The specific gravity of a gem is its weight when compared with the same volume of water at a temperature of 4 degrees Celsius. Minerals composed of heavy elements will have a higher specific gravity than those composed of lighter elements, although bonding and crystalline structure can also effect the specific gravity. 2. Hardness: The hardness of the mineral refers to its resistance to scratching and abrasion and also to the cutting resistance. The more resistant the surface is to scratching, the harder the mineral, and the stronger the bonding forces are holding the atoms together. 3. Cleavage and Fracture: Cleavage and fracture refer to the characteristic manner in which gems will break when an external force or stress is applied. Those with the least tendency to cleave include garnets, quartz, spinel (natural), beryl and zircon. Gemstones with a strong tendency to cleave include diamond, fluorite, topaz, peridot, kunzite (spodumene), euclase, sphene, axinite, feldspars, synthetic spinel, dioptase and calcite. 4. Tenacity or Toughness: The tenacity or toughness of a mineral is the resistance to crushing, breaking, or tearing. 5. Magnetism and Electricity: The ability of a mineral to conduct electricity is referred to as electroconductivity. This property is mostly characteristic of minerals with metallic bonding, such as gold, silver, and copper. Those stones which are attracted by a magnet are considered magnetic, such as magnetite and hematite, which contain iron. 6. Thermal Conductivity: Some stones are good conductors of heat, such as quartz, which draws heat away from the body when held and thus feels cold to the touch. Heat is conducted differently in various minerals according to their crystal system. A poor thermal conductor, such as amber, feels warm to the touch because it does not conduct heat away from the body. The surface of a genuine gemstone will de-mist more rapidly than that of glass or an artificial stone. Optical: Color is the most important factor in determining the value of gemstones and it’s the most obvious visual feature, but in fact it is just one of many optical properties, all of which are dependent upon light. 1. Luster: The overall appearance of a gemstone is predominantly determined by how light is reflected off its surfaces, this is known as the 'Lustre' of a gem. 2. Refraction: The speed of light varies in substances. The speed of light is different in air, water, and other dimensions, including minerals and gemstones. Every gemstone refracts at a distinct, individual angle. The angle of refraction is directly related the speed of light in the gemstone. 3. Dispersion: Dispersion is the splitting of white light into the colors of the spectrum. This effect is observable in faceted, transparent, colorless gems, where the white light disperses in the gem and reflects on its inner surfaces, giving the gem a colorful sparkle. 4. Pleochroism: Color changes which are evident when viewed from different angles in gemstones (iolite, alexandrite, andalusite) is called pleochroism. It is very important for the gem cutter to cut a pleochroic stone properly in order to show off the different colors. 6. Refractive Index: The speed of light varies in substances. The speed of light is different in air, water, and other dimensions, including minerals and gemstones. When light travels from one dimension to another dimension, the light bends, or refracts, upon entering the second dimension. Gems with a higher refractive index tend to show more brilliance, since light is bent at a higher angle when it passes into the material. A gemstone is a mineral or rock, which can be used in jewelry after cutting or faceting and polishing. But are all minerals gemstones? Can a rock be a gemstone?
A mineral is a naturally occurring inorganic solid, with a definite chemical composition, and an ordered atomic arrangement. Minerals are typically formed when molten rock, or magma, cools, or by separating out of mineral-rich water, such as that in underground caverns. Mineralogy is a subject of geology specializing in the scientific study of chemistry, crystal structure, and physical (including optical) properties of minerals. Whereas a rock is an aggregate of minerals and need not have a specific chemical composition. There is a science of rocks as well, called petrology which is essential for understanding the formation of the earth. Many minerals form beautiful crystals which are cut, polished or otherwise modified for decorative purposes. These are known as gemstones. Gemstones have their own science as well, called gemology, which is a branch of mineralogy. Gemstones are classified into two categories: * Precious * Semi-Precious Stones There are a number of semi-precious gems, many quite beautiful, but diamonds, rubies, sapphires, and emeralds continue to qualify as "precious." |
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