Gems

Gems

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  GEMS DISCOVER THE BEAUTIFUL LOOSE GEMSTONES
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  OUTLINE INTRODUCTION : What areGems ?? GENERAL CHARACTERISTICS : At a glance WHAT MAKES IT SPECIAL? ABOUT SOME GEMS : To Mesmerize FINALLY : Benefits REFERENCES
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  INTRODUCTION What is aGEM ? Gems are expensive sparkling mineral stones. A Gem can be a Natural, or Synthetic ceramic. There are about 150 of them. It provides a link between Crystallography ,Mechanical testing, solid-state ,physical and inorganic chemistry ,electrical engineering.
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  GENERAL CHARACTERISTICS  150 naturalcompounds used as gems.  Diamonds, emeralds, rubies, and sapphires sell at highest prices Followed by amber, aquamarine, jade, opal, pink topaz, and tourmaline with intermediate values Agate, amethyst, and zircon with lower values  They are inorganic solid .  It possess an orderly internal structure, that is, its atom must be arranged in a definite pattern.  They have definite chemical composition that may vary within specified limits.
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  What makes themspecial and ATTRACTIVE ?? What makes them different from normal stone?? Color : One of the main features. They are many different reasons for these colors. It could be because of their composition. Cr makes emerald GREEN and rubies RED. Refractive Index : The higher the value of the refractive index of a properly cut gem ,within limits, the more light will return to the eye of the viewer, resulting in its BRILLIANCE. Diamond has a particularly high value of n=2.417.
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   Dispersion : Dispersioncauses rays of light to be split into their colored components that can emerge in slightly different directions. The dispersion is 0.044 for diamond, one of the highest values for a natural gemstone. Color is related to the wavelength of light and dispersion experienced by it.
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   Absorption : Theother factor that is particular to different materials is the optical absorption .The absorption spectrum can easily distinguish different gems. Hematite is gray unless the light passes through it ,in which case it appears red. (hence its name). The reason for the red color is that hematite absorbs blue light. Some gemstones can be identified by the spectral colors they produce Ruby colored by chromium Almandine garnet colored by iron
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   Facets: The facetedgemstone is ideally shaped to optimize its sparkle, i.e., maximize the amount of light that is reflected back to the observer. The object of faceting is to make the most of total internal reflection.  Pleochroism : When ‘n’ of a crystal varies with the direction in which light travels through it, the absorption can be different in different directions. The crystal then shows a different color when viewed in different direction. If there are two distinct directions, the gem’s crystal structure is dichroic, it can be trichroic too.
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  This is whatmakes them expensive A Diamond is Forever !! BeautyBeauty RarityRarity TraditionTradition Perception ofPerception of permanencepermanence
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  OTHER PROPERTIES  Hardness: Diamondis so hard ,it is used to cut glass and other diamonds even. Diamond is the- hardest natural material, 140 times harder than corundum The hardness of a gemstone is referred to as its Mohr’s hardness. The test is called Mohr’s hardness test.  Chemical stability: Gemstones are always thought to be stable ,but some of them are not so stable. Opal contains a significant amount of water ; if this water is removed , then the opal will fracture and degrade. Emeralds are slightly different in that they usually already contain many fractures that have been filled with oil or polymer. Diamond is durable .
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  DIAMONDS AND ASSUMPTIONS AROUNDIT !! Why diamond??, yes ,its hard ,but its optical qualities that have made it so popular !! It can get us good understanding about gems as it is definitely not unheard of !!!  It doesn’t have the best optical properties. The refractive index of diamond is 2.42 whereas the refractive index of moissanite and rutile are 2.69 and 2.65 .  The common assumption is gems are poor conductors of heat ,but diamond is actually a much better thermal conductor than Cu.
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  De Beers inAfrica is the largest supplier of rough diamonds in the world. Measured in carats.
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  Diamond mine. Openpit of International Pipe in Yakutia, Siberia. Both photos by Jim Shigley. © 1995 Gemological Institute of America (GIA). Gem- rare, beautiful, durable A typical diamond deposit yields ~ 5 grams of diamond per 1000 kg of rock mined
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  RUBIES & SAPPHIRES It’s mainlyAl203. If the stone is RED ,it is called ruby ; If it is any other color, it is called sapphire or fancy sapphire. There are many ways to produce the color, Ruby is Cr doped ,while the blue gemstones contain the Fe-Ti complex Sapphires can be colored using dopants . Doping with Be is quite new. The Corundum Group
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  EMERALD AND BERYLS The mineral isgenerally referred as BERYL. It is the principal source of Be. It occurs in three forms : Emerald , Precious Beryl , Aquamarine. The formula Be3Al2Si6O18.(with up to 1H2O); It has n=1.595. The crystal structure is hexagonal and is composed of 6-fold rings of SiO4 tetrahedra, which make up the Si6O18 unit.
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  OPAL Natural opal aredeposited in fissures in rocks or fossilized wood. They consist of perfect arrays of identical spheres of SiO2. The spheres have a radius of about 300nm,so arrays of the spheres look like crystals to incident visible light .Thus the light is diffracted , which is why we see different colors when viewing opal from different directions. The spheres can be amorphous or partially crystalline. Not all opal shows these colors since the term opal refers to any material made up of such SiO2 spheres;
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  OTHER GEMS !! Quartzcrystals are known by different names. The colorless form is known as rock crystal. Amethyst is a single-crystal quartz. The crystals grew naturally by a hydrothermal process The purple color can be used by Fe that is in the +4 state due to natural or artificial irradiation or by Mn. When heat treated, the stones become yellow-orange-brown and are known as citrine
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  TOPAZ  It isa silicate with general formula Al2SiO4(F2OH)3. It is the hardest silicate, the crystal is unusual .It is orthorhombic consisting of chains of AO6 octahedra linked with SiO4 tetrahedra.  It is found in a variety of shades of blue and the imperial yellow. The stones may be radioactive after some days of processing.
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  ARE THESE ONLYFOR DECORATIVE PURPOSE ??  Tourmaline crystal is used to study Double refraction. And the concept of double refraction is useful in LCD’s  Piezoelectricity : electricity can be induced in quartz crystals ,when electric field is applied to induce dimensional change.  Healing crystals and gemstones are one of the most beautiful ,mystical ,and profound “energy medicine”, a tool which have been used since ages. Like yellow sapphire is beneficial for people having fever , cough, rheumatism etc. It is believed to be so !!
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  Thank you !!!