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Gemology
- 1. SOMAVILLE UNIVERSITY Lecturer: IbrahimMohamed Omar “Salihi” SHORT COURSE ABOUT GEMOLOGY FACULTY OF PETROLEUM ENGINEERING CONFIDENTIAL
- 2. What is gemology? Gemologyor gemmology is the science dealing with natural and artificial gemstone materials. It is considered a geoscience and a branch of mineralogy. Some jewelers are academically trained gemologists and are qualified to identify and evaluate gems.
- 3. What is gemstone? Agemstone is the naturally occurring crystalline form of a mineral, which is desirable for its beauty, valuable in its rarity and durable enough to be enjoyed for generations.
- 4. A gemstone orgem (also called a fine gem, jewel, or a precious or semi-precious stone) is a piece of mineral crystal, which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli) or organic materials that are not minerals (such as amber or jet), are also used for jewelry, and are therefore often considered being gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone. Apart from jewelry, from earliest antiquity engraved gems and hard stone carvings, such as cups, were major luxury art forms. A gem maker is called a lapidary or gem cutter; a diamond worker is a diamantaire.
- 5. What is theHardness of Mohs Scale? The Mohs scale of mineral hardness is a qualitative ordinal scale that characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in materials science, some of which are more quantitative.The method of comparing hardness by seeing which minerals can visibly scratch others, however, is of great antiquity, having been mentioned by Theophrastus in his treatise On Stones, c. 300 BC, followed by Pliny the Elder in his Naturalis Historia, c. 77 AD. While greatly facilitating the identification of minerals in the field, the Mohs scale does not show how well hard materials perform in an industrial setting. Moh’s Scale of the precious and semi-precious gemstones
- 6. 10. Diamond 9. Corundumor Ruby and Sapphire 8. Emerald, Aquamarine, Alexandrite, Beryl, Topaz, Jade & etc 7. Tourmaline, Garnet, Quartz, Opal and etc 6. Orthoclase feldspar 5. Apatite 4. Fluorite 3. Calcite 2. Gypsum 1. Talc
- 7. Requirements of GoodQuality Gemstone •Transparent To be applicable to pass through light wholly, this makes to the stone very beauty. •No Cracks The crack is to get inside the stone in tears that causes to uncut to the stone for the reason of this cracks in it. •No Inclusion and no Rutile In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation. In gemology, an inclusion is a characteristic enclosed within a gemstone, or reaching its surface from the interior. According to Hutton's law of inclusions, fragments included in a host rock are older than the host rock itself.
- 8. Precious Gemstones •Diamond •Ruby •Sapphire •Emerald Semi PreciousGemstones •Topaz •Zircon •Spinal •Beryl group excluding Emerald •Tourmaline •Garnet •Quartz •Opal
- 9. •DIAMOND Hardness: 10 Compositions:Carbons Diamond is the hardest mineral on Earth , this combined with its exceptional luster and brilliant fire , has made it the most highly prized of all gems ,pure , colorless diamond is the most popular, but other varieties – from yellow and brown to green, blue, pink, red, grey, and black – are also found, depending on the impurities present. Because of the uniform arrangement of their constituent carbon atoms, diamond crystals are well – formed – usually octahedral with rounded edges and slightly convex faces their perfect cleavage facilitates the early stages of fashioning but they can only be polished by other diamonds, •OCCURRENCE Diamond forms at high temperatures and pressures 80km (50 miles) more underground most Diamond came from second sources , such as rivers and gravels, however , since discovery of diamond in kimberlitic rock in south Africa (around 1870),its extraction has involved processing vast quantities of rock, Australia is the main producer today: other localities include Ghana Sierra Leone, Zaire, Botswana, Namibia, the former USSR, the USA, and Brazil,
- 10. Diamond Clarity Key Points •Clarityis a measure of the number and size of the tiny imperfections that occur in almost all diamonds. •Many of these imperfections are microscopic, and do not affect a diamond's beauty in any discernible way. Much is made of a diamond's clarity, but of the Four Cs, it is the easiest to understand, and, according to many experts, generally has the least impact on a diamond's appearance. Clarity simply refers to the tiny, natural imperfections that occur in all but the finest diamonds. Gemologists refer to these imperfections by a variety of technical names, including blemishes and inclusions, among others. Diamonds with the least and smallest imperfections receive the highest clarity grades. Because these imperfections tend to be microscopic, they do not generally affect a diamond's beauty in any discernible way.
- 11. Diamond Clarity Flawless, InternallyFlawless: No internal or external imperfections. Internally Flawless: No internal imperfections. Very rare. Very, Very Slightly Included: Very difficult to see imperfections under 10x magnification. An excellent quality diamond.' VVS1, VVS2 FL, IF
- 12. Very Slightly Included:Imperfections are not typically visible to the unaided eye. Less expensive than the VVS1 or VVS2 grades.' Slightly Included: Imperfections are visible under 10x magnification, and may be visible with the unaided eye. A good diamond value.' SI1, SI2 VS1, VS2
- 13. I1 Included: Blue Nileoffers a limited selection of jewelry with diamonds of I1 grade clarity. This grade of diamonds will have minor inclusions that may be visible to the unaided eye.' I2, I3 What Clarity Grade Is Right For Me? •Select an "eye-clean" diamond - one that has no imperfections visible to the unaided-eye through the crown. An excellent value, diamonds of this clarity are much less expensive than flawless (FL) or internally flawless (IF) diamonds, which are extremely rare and command higher prices. •Frequently, imperfections in diamonds graded slightly included (SI) are not visible to the unaided eye, making them an excellent value. If you're considering a diamond with an SI clarity grade, call to speak to a diamond and jewelry consultant who will review the diamond to ensure the imperfections are not visible to the unaided eye.
- 14. •RUBY Hardness: 8 Composition:Aluminium oxide Ruby the given to red, gem-quality corundum – is one of the best gemstones for jewellery settings. Rubies may be any shade of red, from pinkish to purplish or brownish red, depending on the chromium and iron content of the stone •OCCURRENCE Worldwide in igneous and metamorphic rocks, or as water worm pebbles in alluvial deposits The finest stones come from Burma
- 15. •SAPPHIRE Hardness 9 CompositionAluminium oxide All gem quality corundum that is not red is called sapphire, yet this name is popularly associated with the colour blue, but most valuable is the clear, deep blue some stones called “colour”-change sapphire “,exhibit different shades of blue in artificial and natural light. •OCCURRENCE Good quality sapphire is found in Burma, Sri lank, and India, The best Indian sapphire is cornflower blue, and found in Kashmir either in pegmatite’s or as wter worm pebbles in alluvial deposits sapphire from Thailand, Australia, and Nigeria is dark blue, and may appear nearly Black Montana (USA) producers sapphire of an attractive metallic blue Other localities include Cambodia, Brazil, Kenya, Malawi, and Colombia,
- 16. •EMERALD Hardness: 8 Composition:Beryllium Chromium Vanadium Aluminium Silicate Emerald derives its beautiful green colour from the presence of chromium and vanadium Emeralds are rarely flawless, so stones are often oiled to fill and disguise cracks, hide flaws and enhance colour to minimize the loss of material, the step cut (or “emerald- cut”, as it is known) is commonly used, but ancient engravings are known, cameos, intaglios, and beads can make the best of a flawed stone. •OCCURRENCE found in granites, pegmatite’s, and schist as well as alluvial deposits the finest emerald are from Colombia, Other sources are Australia India Austria, Brazil, South Africa, Egypt , USA, Norway, Pakistan, and Zimbabwe
- 17. •TOPAZ Hardness: 8 Composition:Alluminium Flouro hydroxy ilicate Topaz occurs in range of deferent colours deep golden yellow topaz (sometimes called sherry topaz) and pink topaz are the most valuable: blue and green stones are also popular. Natural pink stones are rare most pink topaz is heat-treated yellow material •ZIRCON Hardness 8 Composition Zirconium silicate Zircon is almost famous for its colour less stones which closely resemble diamond and have been used both intentionally and mistakenly in their place •OCCURRENCE Gem quality crystals are usually found as pebbles in alluvial deposits
- 18. •SPINEL Hardness: 8 Compositions:Magnesium Allumnium Oxide SPINEL is found in a wide range of colours due to the presence of various impurities andis transparent to almost opaque red spinel coloured by chromium and iron is the most popular, although for many years it was thought to be a variety of ruby •OCCURRENCE spinel occurs in granites and metamorphic rocks, and is often found in association with corundum Octahedral crystals and waterworm pebbles in a wide range of of colours are found in the gem gravels of Burma, Srilanka and Madagascar •REMARK synthetic spinel has been manufactured since 1910it has been used to imitate diamond, coloured to imitate stones such as aquamarine and zircon, blue synthetic spinel, coloured by cobalt, has been used to imitate sapphire The name may derive from the Latin word spina, meaning little thorn, referring to the sharp points on the crystals,
- 19. •BERYL Hardness: 8 Composition:Beryllium Aluminium Silicate Beryl derives its beautiful multi colures from the deserted of chromium and vanadium Beryl are rarely flawless, so stones are often oiled to fill and disguise cracks, hide flaws and enhance colour to minimize the loss of material, the step cut (or “emerald-cut”, as it is known) is commonly used, but ancient engravings are known, cameos, intaglios, and beads can make the best of a flawed stone. •OCCURRENCE found in granites, pegmatite’s, and schist as well as alluvial deposits the finest emerald are from Colombia, Other sources are Australia India Austria, Brazil, South Africa, Egypt , USA, Norway, Pakistan, and Zimbabwe There are many types of group beryl:- •Red Beryl •Morganite Beryl •Goshonite Beryl •Aquamarine Beryl •Beryl •Alexandrite Beryl
- 20. •TOURMALINE Hardness: 7 Composition:Complex borosilicate Members of the tourmaline family of the minerals have the same basic crytal structure, but occur in many colours. Rubellite (from the latin for red) is the name given to the pink or red variety with ruby- red stones the most highly prized. Rubellite crystals are striated, with triangular cross-section and a rounded outline they may also occur with a fibrous habit, and and show cat’s eye when en cabochon. There are many types of tourmaline:- •Rubellite Tourmaline: read tourmaline •Elbite Tourmaline: blue tourmaline •Indicolite Tourmaline: green tourmaline •Watermelon Tourmaline: green and red mixed tourmaline •Bi color Tourmaline: any two colors mixed tourmaline •Paraiba Tourmaline: light blue tourmaline is the rarest type of tourmaline
- 21. •GARNET Hardness: 7 Composition:Magnesium Aluminium Silicate Garnet the blood red colour of pyrope is due to its iron and chromium content, it rarely has inclusions , but when present they are rounded crystals or have irregular out lines ,As with all garnets, pyrope has no cleavage, and fracture is subconchoidal to uneven •OCCURRENCE Pyrobe is found in volcanic rock and alluvial deposits, and may along with certain other minerals, indicate the precence of diamond bearing rocks localities include Arizona (USA), South Africa, Argentina , Australia, Brazil, Burma , Scotland, Switzerland, and Tanzania. •REMARK: pyrope come from Gteek pyrops meaning burning. There are many types of Garnet group:- •Rhodolite Garter: dark red garnet •Specertite Garnet: orange garnet •Pyrobe Garnet: blood red garnet •Almandine Garnet: dark coffee garnet •Hessonite Garnet: dark orange garnet •Tsavorite Garnet: green garnet is the most rarest type of garnet group
- 22. •QUARTZ Hardness: 7 Composition:Silicon Dioxide Citrine is the yellow or golden variety of quartz, The yellow coloration, due to the presence of iron, is also responsible for the name, derived from the word “citrus” natural citrine is usually a pale yellow but rare: There are three types of quartz:- •Macrocrystalline Quartz Rock Crystal Amethyst Aventurine Eisenkiesel Rose Quartz Tiger's, Hawk's, Cat's Eye
- 23. •Microcrystalline Quartz Jasper •Aventurine •Flint •Heliotrope •Plasma •Tiger's, Hawk's,Cat's Eye •Cryptocrystalline Quartz Chalcedony •Agate •Carnelian •Chrysoprase
- 24. •OPAL Hardness: 6.5 Composition:Silica (SiO2·nH2O) Opal is a hydrated amorphous form of silica (SiO2·nH2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineral oid, unlike crystalline forms of silica, which are classed as minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt. Opal is the national gemstone of Australia.