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A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive mineral, which — when cut and polished — is used to make jewelry or other adornments. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific Jewellery (also spelled jewelry, see spelling differences) is a personal Ornament, such as a necklace ring or bracelet made from Gemstones [1] However certain rocks, (such as lapis-lazuli) and organic materials (such as amber or jet) are not minerals, but are still used for jewelry, and are therefore often considered to be gemstones as well. In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere Organic chemistry is a discipline within Chemistry which involves the scientific study of the structure properties composition reactions, and preparation Amber is Fossil tree Resin, which is appreciated for its color and beauty Jet is a geological material and is considered to be a minor gemstone Most gemstones are hard, but some soft minerals are used in jewelry because of their lustre or other physical properties that have aesthetic value. Lustre (or luster) is a description of the way light interacts with the surface of a Crystal, rock, or Mineral. Rarity is another characteristic that lends value to a gemstone.

A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. The biggest pebble here is 40 mm long (1.6 inches).
A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. The biggest pebble here is 40 mm long (1. 6 inches).

Contents

Characteristics and classification

Gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. Gemology ( gemmology outside the United States) is the Science, Art and Profession of identifying and evaluating Gemstones Technical terminology is the specialized Vocabulary of a field Gemology ( gemmology outside the United States) is the Science, Art and Profession of identifying and evaluating Gemstones The first characteristic a gemologist uses to identify a gemstone is its chemical composition. Gemology ( gemmology outside the United States) is the Science, Art and Profession of identifying and evaluating Gemstones Use in chemistry In Chemistry, the empirical formula of a Chemical compound is a simple expression of the relative number of each type of Atom For example, diamonds are made of carbon (C) and rubies of aluminium oxide (Al2O3). In Mineralogy, diamond is the allotrope of carbon where the carbon atoms are arranged in Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 A Ruby is a pink to blood-red Gemstone, a variety of the Mineral Corundum ( Aluminium oxide) WikipediaNaming Next, many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic. A crystal system is a category of Space groups which characterize Symmetry of structures in three dimensions with Translational symmetry in three directions The cubic crystal system (or isometric) is a Crystal system where the Unit cell is in the shape of a Cube. In Crystallography, the rhombohedral (or trigonal) Crystal system is one of the seven lattice point groups named after the two-dimensional In Crystallography, the monoclinic Crystal system is one of the 7 lattice Point groups A crystal system is described by three vectors. Another term used is habit, the form the gem is usually found in. In Mineralogy, shape and size give rise to descriptive terms applied to the typical appearance or habit of Crystals The many terms used by mineralogists For example diamonds, which have a cubic crystal system, are often found as octahedrons.

Gemstones are classified into different groups, species, and varieties. For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. A Ruby is a pink to blood-red Gemstone, a variety of the Mineral Corundum ( Aluminium oxide) Corundum (from Tamil kurundam குருந்தம் or kuruvindam குருவிந்தம் is a Crystalline form of Sapphire (antique greek hyacinthos refers to gem varieties of the mineral Corundum, an Aluminium oxide (Al2O3 when it is a color other than Emerald (green), aquamarine (blue), bixbite (red), goshenite (colorless), heliodor (yellow), and morganite (pink) are all varieties of the mineral species beryl. Emeralds are a variety of the Mineral Beryl (Be3Al2(SiO36 colored Green by trace amounts Aquamarine (Lat aqua marinā, "water of the sea" is a Gemstone -quality transparent variety of Beryl, having a delicate blue or Turquoise Red beryl (also known as bixbite, red emerald or scarlet emerald) is a red variety of Beryl (emerald Be3(AlMn2(SiO36 The Mineral beryl is a Beryllium Aluminium cyclosilicate with the Chemical formula Be3Al2(SiO36 Morganite, also known as "Pink Beryl" "Rose Beryl" "Pink Emerald" and "Cesian Beryl" is a rare light pink to rose-colored gem -quality The Mineral beryl is a Beryllium Aluminium cyclosilicate with the Chemical formula Be3Al2(SiO36

Gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and lustre. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency Specific gravity is defined as the ratio of the Density of a given solid or liquid substance to the density of water at a specific temperature and pressure typically The Mohs scale of mineral hardness characterizes the scratch resistance of various Minerals through the ability of a harder material to scratch a softer material Cleavage, in Mineralogy, is the tendency of crystalline materials to split along definite planes creating smooth surfaces of which there are several named types A fracture is the (local separation of an object or material into two or more pieces under the action of stress. Lustre (or luster) is a description of the way light interacts with the surface of a Crystal, rock, or Mineral. They may exhibit pleochroism or double refraction. Pleochroism is an Optical phenomenon in which grains of a rock appear to be different colors when observed at different angles under a Petrographic microscope. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray They may have luminescence and a distinctive absorption spectrum. Luminescence is also the title of an album by singer Anggun. Luminescence is Light not generated by high temperatures alone A material's absorption spectrum shows the fraction of incident Electromagnetic radiation absorbed by the material over a range of Frequencies.

Material or flaws within a stone may be present as inclusions. In mineralogy an inclusion is any material that is trapped inside a Mineral during its formation The gem may occur in certain locations, called the "occurrence. "

Value of gemstones

Jewelry made with amber
Jewelry made with amber

There is no universally accepted grading system for any gemstone other than white (colorless) diamond. Amber is Fossil tree Resin, which is appreciated for its color and beauty Diamonds are graded using a system developed by the Gemological Institute of America (GIA) in the early 1950s. Historically all gemstones were graded using the naked eye. The GIA system included a major innovation, the introduction of 10x magnification as the standard for grading clarity. Other gemstones are still graded using the naked eye (assuming 20/20 vision). For the past several hundred years, gemstones have been broken down into two categories; precious and semi-precious. Though today we think primarily of diamond, ruby sapphire and emerald as "precious", these categories are based mainly on fashion and the composition of these two lists has changed frequently over time.

Recently a catchy little phrase, the four c's (color, cut, clarity and carat) was introduced as an aid the help the consumer understand the factors used to grade a diamond. With modification these categories can be useful in understanding the grading of all gemstones. The four criteria carry different weight depending upon whether they are applied to colored gemstones or to colorless diamond. In diamonds, cut is the primary determinant of value followed by clarity and color. Diamonds are meant to sparkle, to break down light into its constituent rainbow colors (dispersion) chop it up into bright little pieces (scintillation) and deliver it to the eye (brilliance). This is a function of cut. In its rough crystalline form, a diamond will do none of these things, it requires proper fashioning and this is called "cut". In gemstones that have color, including colored diamonds, it is the purity and beauty of that color that is the primary determinant of quality.

Physical characteristics that make a colored stone valuable are color, clarity to a lesser extent (emeralds will always have a number of inclusions), cut, unusual optical phenomena within the stone such as color zoning, and asteria (star effects). An optical phenomenon is any observable event which results from the interaction of Light and Matter. Asteria, or star stone (from Gr do-rip star) is a name applied to such Ornamental stones as exhibit when cut en Cabochon a luminous The Greeks for example greatly valued asteria in gemstones, which were regarded as a powerful love charm, and Hellen of Troy was known to have worn star-corundum. Corundum (from Tamil kurundam குருந்தம் or kuruvindam குருவிந்தம் is a Crystalline form of [2]

A factor in determining the value of a gemstone is called water. Water is an archaic term that refers to the combination of color and transparency in gemstones; used hierarchically: first water (gem of the finest water), second water, third water, byewater. [3]

Historically gemstones were classified into precious stones and semi-precious stones. Because such a definition can change over time and vary with culture, it has always been a difficult matter to determine what constitutes precious stones. [4]

Aside from the diamond, the ruby, sapphire, emerald, pearl (strictly speaking not a gemstone) and opal [4] have also been considered to be precious. In Mineralogy, diamond is the allotrope of carbon where the carbon atoms are arranged in A Ruby is a pink to blood-red Gemstone, a variety of the Mineral Corundum ( Aluminium oxide) Sapphire (antique greek hyacinthos refers to gem varieties of the mineral Corundum, an Aluminium oxide (Al2O3 when it is a color other than Emeralds are a variety of the Mineral Beryl (Be3Al2(SiO36 colored Green by trace amounts A pearl is a hard roundish object produced within the soft tissue (specifically the mantle) of a living shelled Mollusk. OPAL ( Open Pool Australian Lightwater reactor) is a 20 megawatt pool-type nuclear research reactor that was officially opened in April 2007 Up to the discoveries of bulk amethyst in Brazil in the 19th century, amethyst was considered a precious stone as well, going back to ancient Greece. Amethyst is a violet variety of Quartz often used as an Ornamental stone in Jewelry. Even in the last century certain stones such as aquamarine, peridot and cat's eye have been popular and hence been regarded as precious. Aquamarine (Lat aqua marinā, "water of the sea" is a Gemstone -quality transparent variety of Beryl, having a delicate blue or Turquoise Peridot (pronunciation /ˈpɛrɪˌdɒt/, /ˈpɛrɪˌdoʊ/ (British English /ˈpɛərɪˌdɑt/ /ˈpɛərɪˌdɑʊ/ (US English is the gem quality variety of forsteritic The Mineral or Gemstone chrysoberyl, not to be confused with Beryl, is an aluminate of Beryllium with the formula BeAl2O4

Nowadays such a distinction is no longer made by the trade. [3] Many gemstones are used in even the most expensive jewelry, depending on the brand name of the designer, fashion trends, market supply, treatments etc. Nevertheless, diamonds, rubies, sapphires and emeralds still have a reputation that exceeds those of other gemstones.

Rare or unusual gemstones, generally meant to include those gemstones which occur so infrequently in gem quality that they are scarcely known except to connoisseurs, include andalusite, axinite, cassiterite, clinohumite and bixbite. Andalusite is an Aluminium nesosilicate Mineral with the chemical formula Al2SiO5 Axinite is a brown to violet-brown or reddish-brown bladed Mineral composed of Calcium Aluminium boro - silicate, (CaFeMn3Al2BO3Si4O12OH Cassiterite is a Tin Oxide Mineral, SnO2. It is generally opaque but is translucent in thin crystals Clinohumite is an uncommon member of the Humite group of Minerals a Magnesium Silicate according to the Chemical formula ( Red beryl (also known as bixbite, red emerald or scarlet emerald) is a red variety of Beryl (emerald Be3(AlMn2(SiO36

Gems prices can fluctuate heavily (such as those of tanzanite over the years) or can be quite stable (such as those of diamonds). In general per carat prices of larger stones are higher than those of smaller stones, but popularity of certain sizes of stone can affect prices. Typically prices can range from 5USD/carat for a normal amethyst to 20,000-50,000USD for a collector's three carat pigeon-blood almost "perfect" ruby.

Grading

In the last two decades there has been a proliferation of certification, not only for diamonds but for gemstones as well. There are a number of [3] reputable laboratories which grade and provide reports on gemstones.

Each laboratory has its own methodology to evaluate gemstones. Consequently a stone can be called "pink" by one lab while another lab calls it "Padparadscha". One lab can conclude a stone is untreated, while another lab concludes that it is heat treated [3]. To minimise such differences, seven of the most respected labs, i. e. AGTA-GTL (New York), CISGEM (Milano), GAAJ (Tokyo), GIA (Carlsbad), GIT (Bangkok), Gübelin (Lucerne) and SSEF (Basel), have established the Laboratory Manual Harmonisation Committee (LMHC), aiming at the standardisation of wording on reports and certain analytical methods and interpretation of results. Country of origin has sometimes been difficult to find agreement on due to the constant discovery of new locations. Moreover determining a "country of origin" is much more difficult than determining other aspects of a gem (such as cut, clarity etc. ) [5].

Gem dealers are aware of the differences between gem laboratories and will make use of the discrepancies to obtain the best possible certificate [3]. One such example is to make use of the differences in country of origin: a sapphire from Kashmir, India (celebrated for its cornflower blue color) commands four times the price of the same stone from Sri Lanka and twice the price as a similar stone from Burma. [6]

Enamelled gold, amethyst and pearl pendant, about 1880, Pasquale Novissimo,, born 1844 - died 1914 V&A Museum number M.36-1928
Enamelled gold, amethyst and pearl pendant, about 1880, Pasquale Novissimo,, born 1844 - died 1914 V&A Museum number M. 36-1928

Cutting and polishing

A few gemstones are used as gems in the crystal or other form in which they are found. Most however, are cut and polished for usage as gemstones. The two main 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 regular intervals at exact angles. A cabochon or cabachon is a Gemstone which has been shaped and polished as opposed to Facetted The resulting form is usually a convex top with a A faceting machine is broadly defined as any device that allows the user to place and polish facets onto a mineral specimen Facets are flat faces on geometric shapes The organization of naturally occurring facets was key to early developments in Crystallography, since they reflect the underlying

Stones which are opaque such as opal, turquoise, variscite, etc. OPAL ( Open Pool Australian Lightwater reactor) is a 20 megawatt pool-type nuclear research reactor that was officially opened in April 2007 Turquoise is an opaque blue-to-green Mineral that is a hydrous Phosphate of Copper and Aluminium, with the Chemical Variscite ·2 H2O, hydrated Aluminium phosphate or Berlinite, is a relatively rare phosphate mineral are commonly cut as cabochons. These gems are designed to show the stone's color or surface properties as in opal and star sapphires. Grinding wheels and polishing agents are used to grind, shape and polish the smooth dome shape of the stones. [7]

Gems which are transparent are normally faceted, a method which shows the optical properties of the stone’s interior to its best advantage by maximizing reflected light which is perceived by the viewer as sparkle. There are many commonly used shapes for faceted stones. Diamond Cut is the third album released by Welsh singer Bonnie Tyler in 1979. The facets must be cut at the proper angles, which varies depending on the optical properties of the gem. If the angles are too steep or too shallow, the light will pass through and not be reflected back toward the viewer. Special equipment, a faceting machine, is used to hold the stone onto a flat lap for cutting and polishing the flat facets. A faceting machine is broadly defined as any device that allows the user to place and polish facets onto a mineral specimen [8] Rarely, some cutters use special curved laps to cut and polish curved facets.

Gemstone color

Color is the most obvious and attractive feature of gemstones. The color of any material is due to the nature of light itself. Daylight, often called white light, is actually a mixture of different colors of light. When light passes through a material, some of the light may be absorbed, while the rest passes through. The part that is not absorbed reaches the eye as white light minus the absorbed colors. A ruby appears red because it absorbs all the other colors of white light - blue, yellow, green, etc. - except red.

The same material can exhibit different colors. For example ruby and sapphire have the same chemical composition (both are corundum) but exhibit different colors. Corundum (from Tamil kurundam குருந்தம் or kuruvindam குருவிந்தம் is a Crystalline form of Even the same gemstone can occur in many different colors: sapphires show different shades of blue and pink and "fancy sapphires" exhibit a whole range of other colors from yellow to orange-pink, the latter called "Padparadscha sapphire".

This difference in color is based on the atomic structure of the stone. Although the different stones formally have the same chemical composition, they are not exactly the same. Every now and then an atom is replaced by a completely different atom (and this could be as few as one in a million atoms). These so called impurities are sufficient to absorb certain colors and leave the other colors unaffected. Impurities are Substances inside a confined amount of Liquid, Gas, or Solid, which differ from the Chemical composition of the material

As an example: beryl, which is colorless in its pure mineral form, becomes emerald with chromium impurities. If you add manganese instead of chromium, beryl becomes pink morganite. Morganite, also known as "Pink Beryl" "Rose Beryl" "Pink Emerald" and "Cesian Beryl" is a rare light pink to rose-colored gem -quality With iron, it becomes aquamarine. Aquamarine (Lat aqua marinā, "water of the sea" is a Gemstone -quality transparent variety of Beryl, having a delicate blue or Turquoise

Some gemstone treatments make use of the fact that these impurities can be "manipulated", thus changing the color of the gem.

Treatments applied to gemstones

Treble clef with gemstones
Treble clef with gemstones

Gemstones are often treated to enhance the color or clarity of the stone. Depending on the type and extent of treatment, they can affect the value of the stone. Some treatments are used widely because the resulting gem is stable, while others are not accepted most commonly because the gem color is unstable and may revert to the original tone. [9]

Heat

Heat can improve gemstone color or clarity. Most citrine is made by heating amethyst, and partial heating with a strong gradient results in ametrine - a stone partly amethyst and partly citrine. For the politician of this name see Walter McLennan Citrine 1st Baron Citrine, for the GFP protein derivative see Yellow fluorescent protein. Ametrine, also known as trystine or by its trade name as bolivianite, is a naturally occurring variety of Quartz. Much aquamarine is heat treated to remove yellow tones, change the green color into the more desirable blue or enhance its existing blue color to a purer blue. [10]

Nearly all tanzanite is heated at low temperatures to remove brown undertones and give a more desirable blue/purple color. A considerable portion of all sapphire and ruby is treated with a variety of heat treatments to improve both color and clarity.

When jewelry containing diamonds is heated(for repairs) the diamond should be protected with boracic acid; otherwise it could be burned on the surface or even burned completely up. When jewelry containing sapphires or rubies is heated(for repairs) it should not be coated with boracic acid or any other substance, as this can etch the surface; it does not have to be "protected" like a diamond.

Radiation

Most blue topaz, both the lighter and the darker blue shades such as "London" blue, has been irradiated to change the color from white to blue. Topaz is a Silicate mineral of Aluminium and Fluorine with the Chemical formula Al 2 Si[[oxygen O]]4( Irradiation is the process by which an item is exposed to Radiation. Some improperly handled gems which do not pass through normal legal channels may have a slight residual radiation, though strong requirements on imported stones are in place to ensure public safety. Most greened quartz (Oro Verde) is also irradiated to achieve the yellow-green color.

Waxing/oiling

Emeralds containing natural fissures are sometimes filled with wax or oil to disguise them. This wax or oil is also colored to make the emerald appear of better color as well as clarity. Turquoise is also commonly treated in a similar manner.

Fracture filling

Fracture filling has been in use with different gemstones such as diamonds, emeralds and sapphires. More recently (in 2006) "Glass Filled Rubies" received a lot of publicity. Rubies over 10 carat (2 g), particularly sold in the Asian market with large fractures were filled with lead glass, thus dramatically improving the appearance (of larger rubies in particular). Such treatments are fairly easy to detect.

Synthetic and artificial gemstones

Some gemstones are manufactured to imitate other gemstones. For example, cubic zirconia is a synthetic diamond simulant composed of zirconium oxide. Cubic zirconia (or CZ) the cubic crystalline form of Zirconium dioxide ( ZrO2) is a Mineral that is widely synthesized This article addresses the many imitations of diamond For a broader discussion of diamonds see Diamond. Zirconium (zɚˈkoʊniəm /ˌzɝˈkoʊniəm/ is a Chemical element with the symbol Zr and Atomic number 40 The imitations copy the look and color of the real stone but possess neither their chemical nor physical characteristics.

However, lab created gemstones are not imitations. For example, diamonds, ruby, sapphires and emeralds have been manufactured in labs to possess identical chemical and physical characteristics to the naturally occurring variety. A Ruby is a pink to blood-red Gemstone, a variety of the Mineral Corundum ( Aluminium oxide) Sapphire (antique greek hyacinthos refers to gem varieties of the mineral Corundum, an Aluminium oxide (Al2O3 when it is a color other than Emeralds are a variety of the Mineral Beryl (Be3Al2(SiO36 colored Green by trace amounts Synthetic (lab created) corundums, including ruby and sapphire, are very common and they cost only a fraction of the natural stones. Corundum (from Tamil kurundam குருந்தம் or kuruvindam குருவிந்தம் is a Crystalline form of Smaller synthetic diamonds have been manufactured in large quantities as industrial abrasives. Synthetic diamond (also known variously as lab-created, manufactured, lab-grown or cultured diamond) is a term used to describe Diamond An abrasive is a material often a Mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away Larger synthetic diamonds of gemstone quality, especially of the colored variety, are also manufactured.

Whether a gemstone is a natural stone or a lab-created (synthetic) stone, the characteristics of each are the same. Lab-created stones tend to have a more vivid color to them, as impurities are not present in a lab, so therefore do not affect the clarity or color of the stone. However, natural gemstones are still considered more valuable on average due to their relative scarcity.

The origin of the gemstone also does not affect its categorization as precious or semi-precious. Rubies, sapphires and emeralds are always precious stones, while other gems are considered semi-precious.

See also

Notes

  1. ^ The Oxford Dictionary Online and Webster Online Dictionary
  2. ^ Burnham, S. A number of Gemstones have gained fame either because of their size and beauty or because of the people who owned or wore them A lapidary (the word means "concerned with stones" is an Artisan who practices the craft of working forming and finishing stone, Mineral, M. (1868). Precious Stones in Nature, Art and Literature. Bradlee Whidden.   Page 251
  3. ^ a b c d e Secrets of the Gem Trade; The Connoisseur's Guide to Precious Gemstones Richard W Wise, Brunswick House Press, Lenox, Massachutes. , 2003 URL: Secrets of the Gem Trade, Official Website (Has several chapters online)
  4. ^ a b Church, A. H. (Professor at Royal Academy of Arts in London) (1905). Precious Stones considered in their scientific and artistic relations. His Majesty's Stationary Office, Wyman & Sons.   Chapter 1, Page 9: Definition of Precious Stones URL: Definition of Precious Stones
  5. ^ [Rapaport report of ICA Gemstone Conferene in Dubai]
  6. ^ [Richard Wise Blog on Christie's sale of Padparadscha Sapphire]
  7. ^ Introduction to Lapidary by Pansy D. Kraus
  8. ^ Faceting For Amateurs by Glen and Martha Vargas
  9. ^ Gemstone Enhancement: History, Science and State of the Art by Kurt Nassau
  10. ^ Nassau, Kurt (1994). Gem Enhancements. Butterworth Heineman.  

External links

Dictionary

gemstone

-noun

  1. a gem, usually made of minerals.
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