Lecture 1 Notes (Geoscience 331)
Lecture 1 Notes (Geoscience 331) Geoscience 331
Popular in Gems: The Science Behind the Sparkle
Popular in Geology
This 3 page Class Notes was uploaded by Hannah James on Monday September 7, 2015. The Class Notes belongs to Geoscience 331 at University of Wisconsin - Madison taught by Huifang Xu in Fall 2015. Since its upload, it has received 167 views. For similar materials see Gems: The Science Behind the Sparkle in Geology at University of Wisconsin - Madison.
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Date Created: 09/07/15
Geo 331 Lecture 1 What is a gem 0 Early gems were often made of organic materials such as Mother of Pearl and bone 0 A gem is a naturally occurring material desired for its beauty valuable in its rarity and durable to give lasting enjoyment 0 There are many different types of gems most of which are quite ordinary looking until they are enhanced I Enhancement often starts with basic cutting and polishing but subjecting a gem to heat or radiation can also produce desirable effects 0 Some gems are synthesized or simulated for commercial purposes 0 Synthetic a gem that is humanmade and has an identical crystalline structure to a natural gem They are made of carbon just like naturallyproduced gems O Simulant a gem that is made to look like another more valuable gem 0 There are many trade an commercial names for gemstones and stimulants that can obscure the identity of a gem and whether it s fake I EX the Siberian quartz crystal is a synthetic crystal with deep blue color What makes a gem desirable I Gems are often enhanced to make them more desirable I A common way to do this is to cut facets into it increasing the brilliance fire and luster of a gem and thus increasing it desirability O Brilliance amount of light re ected at the viewer this is the gems sparkle 0 Fire shows small bands of rainbow color in the gem which are measured by dispersion I Dispersion can be measured accurately so gems that display lots of fire have a higher dispersion and vice versa 0 Luster the surface appearance of a gem and how light is re ected off it I Some gems have a glassy luster like glass some have a waxy or metallic luster etc I The degree of surface polish determines the type of luster on a gem the smoother the surface the more the luster will appear desirable 0 Color the more pure and transparent the color the more valuable O Resisting to scratching durability evaluated gem hardness the more resistant to scratches by dust sand etc the more valuable I There are two measures of hardness scratch and indentation hardness we are more concerned with scratch hardness Anatomy of a cut gem FEELIJII agate1 a plan Plum i5 llH 39 39u I a if 5quot 15 HERLEE H Gill ilf in if 3 a i El J is H h 395 in 4 H I quot xxx wxam 3 il I BE x 39 Lr 11z39l H 391 39 I n39 all 1 iwillw l 39 39 i ray L J 339 7 L h H II H rail 1 a f f a finlczl 0 Crown top part of the gem 0 Girdle widest part of the gem marks division between crown and pavilion 0 Pavilion lower portion of the gem 0 Culet bottommost facet of a gem sometimes referred to as cutlet 0 Table topmost facet of a gem Common types of cuts 0 Cabochon a round or ovalshaped stone that is at on one side often used with opaque gems such as opals and star sapphires Example of a cabochon cut 0 Emerald a boxyshaped cut often used to cut emeralds because of their tendency to be brittle this cut helps to minimize chipping It ll 5133 till El ag llLPm39 5 EU a LilFEE Example of an emerald cut 0 Brilliant a cut designed to maximize the amount of light re ected back to the viewer Example of a brilliant cut Value and the four C s 0 There are four key factors that affect the value of a gemstone 0 Color some colors are more desirable than others O Clarity cracks and inclusions aws lower the value of a gem The more clear a gem is the more valuable it will be 0 Cut properly cut gems maximize fire brilliance durability etc O Carat weight a function of volume density bigger is not always better 0 1 carat 02g5 carats 1g 0 Rarity can also be a factor in the value of a gem 0 Supply of the controlling of supply can also change the value of a gem by changing demand or investment potential by consumers 0 The value of a gem may also be lower if its clarity or color has been altered by treatment heat dyeing etc
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