GEMS. Presented By: Nirmala De Silva. Gems have been part of human history for over 20,000 years.

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1 GEMS Presented By: Nirmala De Silva What is a Gem Gems have been part of human history for over 20,000 years. very early gems were generally of organic materials. Examples coral, amber, and vegetable ivory most gems used today are inorganic minerals. early crystal gems were probably derived from alluvial sources. as found, gems are rather ordinary-looking, unlike cut gemstones there are many different kinds of gems, and most come in many colors gems can be synthesized 1

2 What is a Gem (Contd.) gems can be enhanced (and most commonly are) simulants are different from synthetics names: trade or commercial names obscure the true identity of a gemstone or simulant material A gem is a naturally occurring material desirable for its beauty, valuable in its rarity, and sufficiently durable to give lasting pleasure. Beauty is determined by brilliance, iridescence, color, sparkle, and play of color. A gem should be durable against heat and common household chemicals. It should not be easily scratched or broken. Brittleness is a measure of the gem's tendency to crack or cleave. Gem Formation Earth crust varies from 5km thick under the seabed to 40 km under continents. Under the crust is the mantle, which is approximately 3000 km thick. It makes up 83% of the earth's volume. The mantle is composed of molten rock, called magma. In the rare occasions where it reaches the surface (lava). The mantle is hottest near the center and heat currents keep it in constant motion. Where the mantle and crust meet, is a turbulent zone with high pressures and temperatures. The crust is made up of several plates that float on the liquid mantle. As they run into with each other, some are pushed down; others are raised into new mountains. 2

3 Gem Formation (Contd.) The magma is also in constant motion. Its movement and pressure are constantly acting on the bottom of the crust, creating wear and fracturing. Rocks break free from the crust and are carried away in the fluid magma. Much of this material melts, changing the chemistry of the nearby magma. Some of the smaller particles are destined to be inclusions in future gems. The lower surface of the crust is heavily fractured and contains numerous cavities. Fluids escaping from the magma flow through these fractures and cavities. It is here we find the proper conditions for crystal growth. The fluid is a chemical rich soup, which supplies the necessary ingredients. The cavities offer space to grow and the temperature and pressure are high. As the fluid moves through the crust, it cools enough for crystallization to occur. Only time is still required. Gem Formation (Contd.) The passages are constantly opening and collapsing. Often crystals start to form, and then the passage feeding the fluid is closed off. At this point all growth stops. If the passage reopens, growth will begin again. Often this on and off growth pattern is undetectable in a crystal. Other times, the successive layers of growth will have a slightly different chemical composition. When this happens, color zoning in the crystal will happen. In some occasions, the new layers will have different orientation. This is the cause of twinning. Still other times, the new layers will not bond completely with each other. 3

4 Gem Formation (Contd.) In the on and off growth process, the same minerals need to reform. Indeed, the temperature, pressure, and/or chemistry often vary, producing different minerals. When opening a deposit, it is common to see different minerals covering earlier layers There are three kinds of rock formation; igneous, metamorphic, and sedimentary. Igneous minerals are created with heat. They are minerals that are created deep within the earth. Metamorphic refers to conditions where heat and pressure change existing minerals into something new. Sedimentary rocks are based on deposits of sediment. Gem Formation (Contd.) Since crystals form under the surface, how they get to the top where people can mine them. A few crystals are brought to the surface during volcanic eruptions. However, most reach the surface through mountain building and erosion. Over vast periods of time, the movement of the continental plates causes mountains to rise. Years of weathering take down the mountain, leaving the deposits near the surface. 4

5 Why are gems cut Internal reflection, critical angle Refraction Why are gems cut (Contd.) Light travelling through a stone intersects the stone-air surface. If it passes within the critical angle it will exit the stone. If it passes outside the critical angle, it will be internally reflected. In order to achieve brilliance and sparkle, light should escape from top facets, not from the pavillion. Many gem cuts that meet the basic critical angle requirements can be created. Two important examples are the "Brilliant Cut" and "Emerald Cut". 5

6 Why are gems cut (Contd.) Luster Not only does the placement of the facets matter, but the smoothness of the surface (called "luster") does too. Luster is a function of both the surface and the Refractive Index of the mineral itself. Terms used to describe luster include adamantine, pearly, metallic, silky, vitreous, resinous, and waxy. When the surface of the gem is polished, the light is internally reflected,, as expected. If the surface of the gem is left rough, light is lost through unplanned leakage. Why are gems cut (Contd.) Fire Fire" refers to the rainbow-like flashes of color seen in cut stones. Fire is especially obvious in diamonds. 6

7 Value The 4 factors that affect the value of a gemstone are easily remembered as the "4 c's": Color: : Clearly, color affects value. Some colors are more desirable than t others. In part, this is dictated by personal taste and in part by industry standards (e.g., for diamonds). Clarity: flaws (crack, inclusions) decrease the value of a gemstone. Cut: : the ideal proportions for gems (to optimize brilliance and fire) are not always to be found in a faceted stone. Poorly cut stones have e much lower value. Small errors in the placement of facets decrease the value of a gem. Carat weight: : bigger is not always better, but for otherwise equal color, clarity, cut, the larger the stone will be more expensive! Value (Contd.) 1 carat = 0.2 g, thus 5 carat = 1 g Notice that the number of carats depends on density, so two different types of gems of the same size will normally be a different number of carats! Obviously, the rarity of a gemstone is an important factor in determining the value. However, some other things that affect value that are unrelated to the 4c's and rarity. The supply of a specific type of gem can be controlled to improve the value or a specific gem may greatly change in value due to consumer demand or perceived investment potential. The value of a gem may be much lower if its apparent clarity or color has been improved by treatment. Furthermore, synthetic gems (made by humans) have very much lower values than natural stones and beware! - the gemstone is not always the material it is claimed to be: it may be a simulant (look-alike). 7

8 Gems in Sri Lanka Sri Lanka is home to 40 varieties of Gems out of 85 varieties available ailable in the whole world. "Variety of gem material" that one can find in Sri Lanka are listed below. Corundum - Blue s, Star s, Rubies, Star Rubies, Yellow s, Pink s, Padmadradcha, Orange s, White sapphires. Chrysoberyl Cat's Eye, Alexandrite, Alexandrite Cat's Eye, Chrysoberyl. Spinel Blue Spinel, Red Spinel, Purple Spinel. Topaz White Topaz (When Treated Makes London Blue) Zircon Green Zircon, Yellow Zircon, Brown Zircon, Colourless Zircon. Garnet Rhodolite Garnet, Hessonite Garnet, Pyrope Garnet, Almandine Garnet. Beryl Aquamarine, Heliodor. Quartz Smoky Quartz, White Quartz, Amethyst Quartz Cat's Eye Tourmaline Brown Tourmaline, Yellow Tourmaline (Green & Blue Rare) Feldspar Moonstones Also Andalusite, Kornerupine And A Variety Of Agates. Gems in Sri Lanka (Contd.) Rare Gemstones Sinhalite, Lolite, Indicolite, Fibrolite, Taaffeite, Ekanite and Star Spinel. The Blue is Sri Lanka's Gem Supreme. And Sri Lanka's Blue s are the finest in the world. s of the finest quality q have what is called the experts 'a corn flower blue' or a royal blue tint. The highly priced of all gems, the Blue is second only to the diamond in hardness. The largest known s in the world weighing 42 pounds was found in the gem gravels of Sri Lanka. The world jewelry market demands Blue B s of carats. Sri Lanka's Star s is the star beauty among Earth's precious stones. The most celebrated Sri Lanka's star is on permanent display at the Smithsonian museum of Natural History in New York. However, Sri Lanka has not gotten the recognition it deserves as the stone is named the Star of Bombay. 8

9 Gems in Sri Lanka (Contd.) Moonstone the only gem that is found in situ in Sri Lanka displays a milky bluish sheen similar to that of the moon beams, and hence the name moonstone. Through some quirk of nature, moonstones are found only in a solitary quarter acre block of land in the village of Meetiyagoda. The world's moonstone market is dominated by Sri Lanka. Gem mining in Sri Lanka Estimates are that 90 percent of Sri Lanka is potential gem bearing land - the gem-bearing belt is approximately 80 miles in length and 20 miles in width and lies south-west of the central hills, as well as other pockets of gem producing areas. Sri Lanka offers a concentration of gemstones not found anywhere in the world and is second only to Brazil in hosting the greatest variety of gemstones found worldwide. 9

10 Gem mining in Sri Lanka (Contd.) Heat treatment Heat Treatment Gems, mainly those of the corundum group, are heat treated to enhance the value. Sri Lankans have made some progress in mastering the process of heat treatment and there are several parties engaged in this service. During the period , 11,430 kgs of rough geudas amounting to Rs. 1,675 Million were exported to Thailand. This loss is attributed to lack of technological know-how on heat-treatment treatment and imitation in investment on advanced technology and related equipment. 10

11 Sri Lanka's Gem Exports Year/Item 1997 Rs. Mn Rs. Mn Rs. Mn Rs. Mn Rs. Mn. Cut and Polished Gems Rough Geuda Diamond Jewellery Diamond Jewellery The Danger The British crown sports a 400 carat Sri Lankan blue sapphire. There are still more than 3,000 gem mines in Sri Lanka but some argue the future of the industry lies in developing a processing centre for high end precious stones which need specialized cutters with considerable experience. The argument is that the country produces the best sapphire in the world and they should be branded as a purely Sri Lankan product just like Ceylon Tea. But others say it's a mistake to stress geography instead of quality - especially when many gemstones in Sri Lanka actually come from Madagascar and Tanzania. Sri Lankan traders now visit Madagascar in particular to buy rough stones which they bring home for cutting and polishing and it's then difficult to establish their origin when they leave the island for export. 11

12 Birthstones by Month Certain stones can bring you good luck according to your month of o birth. January: Garnet February: Amethyst March: Red Jasper, Blood Stone April: Diamond, May: Emerald, Jade, Green Tourmaline June: Emerald, Pearl, Moonstone July: Turquoise, Onyx, Ruby August: Peridot,, Chrysoberyl Cat's Eye September: Chrysoprase,, October: Opal, Aquamarine November: Topaz, Yellow, Citrine, Yellow Zircon December: Ruby, Turguoise Stones for Days of the Week Follow this weekly schedule for good luck! Sunday: Ruby Monday: Moonstone Tuesday: Coral Wednesday: Emerald Thursday: Chrysoberyl Cat's Eye Friday: Diamond Saturday: Blue, Black Pearl 12

13 13 Stones for Stones for Lagna Lagna Yellow Yellow Jupiter Jupiter Pisces Pisces Blue Blue Satun Satun Aquarius Aquarius Blue Blue Satun Satun Capricon Capricon Yellow Yellow Jupiter Jupiter Sagittarius Sagittarius Coral Coral Mars Mars Scorpio Scorpio Diamond Diamond Venus Venus Libra Libra Gem Stone Gem Stone Ruling Ruling Planet Planet Lagna Lagna Emerald Emerald Mercury Mercury Virgo Virgo Ruby Ruby Sun Sun Leo Leo Pearl Pearl Moon Moon Cancer Cancer Emerald Emerald Mercury Mercury Gemini Gemini Diamond Diamond Venus Venus Taurus Taurus Red Red Coral Coral Mars Mars Aries Aries Gem Gem Stone Stone Ruling Ruling Planet Planet Lagna Lagna Thank You Thank You