Lecture 6 Notes (Geoscience 331)
Lecture 6 Notes (Geoscience 331) Geoscience 331
Popular in Gems: The Science Behind the Sparkle
Popular in Geology
This 2 page Class Notes was uploaded by Hannah James on Thursday October 8, 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 34 views. For similar materials see Gems: The Science Behind the Sparkle in Geology at University of Wisconsin - Madison.
Reviews for Lecture 6 Notes (Geoscience 331)
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 10/08/15
II The Silicates Quartz and other varieties of Si02 Lecture 6 May the Quartz be with you The most abundant elements in the earth s crust are oxygen 0 and silicate Si Silicates are the largest and most varied groups of minerals and they are all based on the siliconoxygen tetrahedron SiO4 which is the building block for all silicates Quartz is the most basic Si02 0 It is colorless when pure but impurities create all the colors we associate with quartz Quartz basic data 0 Chemical Formula Si02 Mohs39 hardness 7 Crystal System Hexagonal or trigonal Color Many see varieties Fracture Conchoidal Specific Gravity 265 Refractive Index Low 154 Luster Vitreous Glassy Interesting Property Piezoelectric forms an electric charge when pressure is 00000000 applied to it does funny things when given a charge I Quartz will ex when given a charge alternating currents will cause it to move back and forth Quartz is found in igneous sedimentary and metamorphic rocks 0 It is hard lacks cleavage and is chemically stable thus it does not weather Flint quartz was the first mineral fashioned into tools and weapons Varieties O Quartz is divided into two broad categories I Coarsely crystalline I Referred to as quartz I Cryptocrystalline I Referred to as chalcedony or chert 0 These categories differ in formation grain size impurities etc Coarsely Crystalline Varieties Ex rock crystal amethyst citrine smoky quartz etc 0 Color depends on impurities Rock crystal colorlessnot often used as a gem clear and can be used in microscopes Amethyst iron gives amethyst its characteristic color in cut stones alternating bands of colors may be seen 0 Heat treatment is often used to remove a smoky appearance III IV Citrine transparent orange and yellow quartz also demonstrates zonation in color can be created by heat treating amethyst Smoky Quartz greyblack quartz gets its color from aluminumoxygen charge transfer Rose Quartz pink comes from small amounts of titanium Milky Quartz appearance due to inclusion often of uid Rutilated Quartz normally clear quartz that contains fine rutile crystals Ti02 Cryptocrystalline Quartz Fibrous varieties O Carnelian orangebrownred from hematite chrysoprase yellow from nickel agate layered bands of varying colors Granular varieties O Jasper opaque red green blue or black from ironoxide bloodstone jasper with green body color and red inclusions Opal Opal is an amorphous silicate no crystalline structure yet displays internal order 0 Formed from balls of amorphous silica sizespacing of balls affect wavelengths of light Opal Varieties three groups 0 Precious Opal two subgroups I Display opalescence spectral color iridescence changes with angle I White Opal 0 An opaque stone in which colors appear as ashes or speckles I Black Opal I Contains fire with a dark body color less common more costly 0 Fire Opal I Transparent or translucent with an orange or red body color named for their color but are not opalescent 0 Common Opal I Opaque many names used to describe varieties Opal is formed by circulating groundwater or lowtemperature hydrothermal solutions 0 It linesfills cavities in rock near the surface 0 India and Eastern Europe were historically the sites to find opal but now most of it comes from Australia Opal Enhancements O Doublets and Triplets a thin slice of opal cemented to a dark substrate less expensive than precious opal O Opal treatments surface oiling heating etc 0 There is both synthetic opal and stimulants of opal glass slocum stone
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'