Gemstones week of 2-3
Gemstones week of 2-3 1108
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This 3 page Class Notes was uploaded by Caroline Bacevice on Thursday February 5, 2015. The Class Notes belongs to 1108 at Ohio State University taught by Loren Babcock in Spring2015. Since its upload, it has received 53 views. For similar materials see Gemstones in Earth Sciences at Ohio State University.
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Date Created: 02/05/15
Gemstones Week of 23 Crystals Crystal a solid having a regular internal arrangement of atoms or ions and at faces geometrically arranged outer surfaces Contrast with o Amorphous gems noncrystalline no at faces I Ex opal glass plastic Crystal vs crystal As a scientific term A solid having at faces As a colloquial term A clear colorless glass resembling rock crystal which is quartz 0 Ex Waterford crystal Swarovski crystal watch crystal 0 These are actually amorphous solids o In gemology glass is referred to as glass or paste To understand Crystals you need to know some basic mineralogy and crystal chemistry What are crystals made of Elements that compose or give color to most of the important gems 0 Construct Minerals silver aluminum oxygen carbon calcium 0 Coloration Nitrogen Boron Titanium Beryllium Fluorine Chromium Copper Lithium Vanadium What are the major groups of minerals Silicates sirich minerals o Quartz Beryl tourmaline garnet peridot Oxides O is the anion negatively charged ion 0 Corundum alexandrite Carbonates C and O o Calcite aragonite pearls Elements 0 Diamond C gold Au Silver Ag Platinum Pl How are crystals held together Atomic bonding o Ions form when atoms gain or lose electrons I Anion negatively charged ion I Cation positively charged ion 0 Ionic bond Electrons are exchanged I Relatively weak bond I Salt NaCl 0 Covalent bond electrons are shared I Strongest bond I Quartz Other Types of bonds Van der Waals bonds weakest bonds 0 Makes minerals soft or easily breakable along cleavage planes Metallic Bond Electrons are free to travel throughout the substance 0 Fives metals their cohesiveness malleability ductility heat conductivity and electrical conductivity How are crystal formed A crystal is built by arranging atoms in a regular power Unit Cell basic arrangement of atoms in a crystalline structure The unit cell is a repeated to fin a crystal Polymorphs Minerals having the same chemical composition but different crystal structures Crystal Symmetry Symmetry Faces on a crystal have a symmetry because of the arrangement of atoms Important for 0 Identifying minerals in uncut form 0 Determining the best way to cu a crystal Crystal Systems Cubic At least four threefold axes of symmetry 0 Diamond or Garnet gold silver platinum Hexagonal threefold or sixfold symmetry 0 Beryl sapphire ruby emerald aquamarine quartz Tetragonal One fourfold axis of symmetry 0 Zircon Orthorhombic At least three twofold axes of symmetry 0 Topaz Monoclinic At least one twofold axis of symmetry 0 Orthoclase Feldspar Triclinic no axis of symmetry 0 Amblygonite What gives minerals their colors One important source of color 0 Body color due to the internal chemical composition of a stone Idiochromatic gems self coloredquot Colorcausing elements are an essential part of the chemical composition of the stone 0 Ex rhodolite red garnet Allchromatic gems Colored by impurities gems are colorless when pure 0 Ex Corundum How Can Gems be identified Physical and optical properties of minerals Phsycical observations on uncut gems Hardness Mohs scale Cleavage Preferential breakage along some surfaces where atomic bonds are weaker Fracture Breakage along a surface that is not related to its internal atomic structure Streak Color of powdered mineral when scraped across a streak plate unglazed tile Crystal Shape 0 Crystal Symmetry o Other Shapes I Pyramidal prismatic I Acicular needle like I Massive no crystal habit I Dendritic branch like I Amorphous no crystal shape I Twin internal structure of crystal is repeated Observations on cut and uncut gems Color color change pleochroism Fluorescence Luster Specific Gravity Refractive Index Dispersion Various Phenomena cat s eye effect star effect etc Optical Properties isotropy anisotropy Heat and electrical conductivity
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