81. Rockhounding Arkansas, Table Of Contents An authoritative, comprehensive reference for Arkansas minerals and the hobby Collecting crystals, the Guide to Quartz in Arkansas is available from A I http://rockhoundingar.com/contents.html

Rocks and minerals, quartz crystals, diamonds; rockhounding in Arkansas offers many opportunities Helpful beginners tip: Bookmark this page! You'll want to come back and read more Meet our geologist in residence: Mike Howard HEIGHT="31" WIDTH="88" NATURALSIZEFLAG="0" ALIGN="BOTTOM" ALT="Webtracker"> Arkansas Weather Read more about rockhounding with books from If you are a beginner or an accomplished mineralogist, you'll want to read through the stories and information presented here for the enjoyment of this fascinating hobby. Rockhounding Arkansas is presented by Mike and Darcy Howard, for your information and enjoyment of mineral collecting. Mike has authored numerous articles and publications for collectors as well as for the scientific community. The companion book to our website. Collecting Crystals, the Guide to Quartz in Arkansas Chapter 1. This chapter is one of the most comprehensive and authoritative references you will find on quartz, from Arkansas or otherwise. Quartz is Arkansas' most famous mineral. Known around the world, your collection is not complete without an Arkansas Quartz crystal. Chapter 2.

82. Igneous Rocks - Basic Course In Geology Since rocks mixtures of minerals, they behave somewhat differently. The processes is called magmatic differentiation by crystal fractionation. http://www.earthsci.org/teacher/basicgeol/igneous/igneous.html

Magmas, Igneous Rocks, Volcanoes, and Plutons Earth Science Australia... Contents of Entire Course of "The Earth and Beyond Kinds of Igneous Rock Types of Magma ... Plutons adapted to HTML from lecture notes of Prof. Stephen A. Nelson Tulane University Kinds of Igneous Rock top... Igneous Rocks are formed by crystallization from a liquid, or magma. They include two types Volcanic or extrusive igneous rocks wherein the magma cools and crystallizes on the surface of the Earth Intrusive or plutonic igneous rocks wherein the magma crystallizes at depth in the Earth. Magma is a mixture of liquid rock, crystals, and gas. Characterized by a wide range of chemical compositions, with high temperature, and properties of a liquid. Magmas are less dense than surrounding rocks, and will therefore move upward. If magma makes it to the surface it will erupt and later crystallize to form an extrusive or volcanic rock . If it crystallizes before it reaches the surface it will form an igneous rock at depth called a plutonic or intrusive igneous rock . Because cooling of the magma takes place at a different rate, the crystals that form and their interrelationship (texture) exhibit different properties.

83. Geology Basics: Rocks And Minerals, Plate Techtonics, Climate History geology Basics Rocks and minerals, Plate Tectonics, Climate History, Surface Water Because crystal structures are unique to a mineral, a mineral can be http://www.acad.carleton.edu/curricular/GEOL/classes/geo120/geology_basics.htm

Geology Basics: Rocks and Minerals Plate Tectonics Climate History Surface Water and Groundwater This page is meant to serve as a preliminary source of information for geology concepts not covered in your textbook. For more complete explanations, the geology textbook Understanding the Earth by Frank Press and Raymond Siever is on closed reserve. The following information is adapted from that text. In addition, there are CD-ROMs which take you through all of the concepts and have animated demonstrations. Rocks and Minerals: Minerals – A mineral is a naturally occurring, solid crystalline substance, generally inorganic, with a specific chemical composition. (26) In a mineral, the constituent atoms are bonded together in a specific, ordered lattice. The way in which a combination of atoms bonds depends on the atomic properties of each element. Different minerals are classified based on a combination of their chemical composition and their crystal structure. Follow this link for more information on the chemical properties of minerals . Because crystal structures are unique to a mineral, a mineral can be identified by the shape of its faces and by its cleavage, or the planes along which it tends to break. This link has information about all the

84. Geological Sciences 101 Other constraints on the combination of atoms to form minerals are the size Cooling rate affects crystal size, thus the fastcooling volcanic rocks are http://www.geo.cornell.edu/geology/classes/Geo101/101week8_f01.html

Introduction to Geological Sciences Week 8 In Class Slides shown in class In Lab Lab 8 Gem and Mineral Photo Gallery at the Smithsonian Institution Links to good stuff... Cornell's Atlas server Interactive Geological Timescale Science in the news, courtesy of USA Today CNN Nature ... List of Geoscience Internship Opportunities Review Rocks and Minerals Most rocks are made up of silicate mineralsin fact, with the exception of limestonevirtually all rocks are silicates. The basic building block of the silicate structure is the silicate tetrahedrona pyramid-shaped unit with one Si at the center surrounded by four oxygen atoms. These tetrahedra link together and combine with additional elements such as Fe, Al, Ca etc. to form the different silicate minerals. The important silicate mineral groups are organized into a scheme called Bowen's Reaction Series. BRS indicates the order in which minerals would crystallize out of a basaltic magma, and shows that (for the most part) the early-forming, high-temperature minerals are those with simple structures, while the latest-forming, lowest-temperature minerals have the most complicated structures. Minerals that occur near each other on BRS also occur together in igneous rocks. Minerals high on BRS are called mafic and so are the rocks that they form. Mid-level minerals are intermediate; the lowest minerals are felsic and form the felsic igneous rocks.

85. Sedimentary, Metamorphic, Igneous Rock Types [Athro, Limited: Geology] When a magma cools rapidly, mineral crystals do not have time to grow very large. When a magma cools slowly crystals grow to several millimeters or more in http://www.athro.com/earth_science/rocks.html

Athro, Limited Earth Science Rock Types The major Rock Types and how they form Igneous Rocks Basalt Granite Igneous rocks solidify from a liquid magma as it cools. They are described on two axies: 1) Rocks that are quartz rich ( felsic ) to magnesium rich ( mafic ) and 2) fast cooling (small crystals) to slow cooling (large crystals). When a magma cools rapidly, mineral crystals do not have time to grow very large. When a magma cools slowly crystals grow to several millimeters or more in size. Granite and basalt are opposites on these axies for the description of igneous rocks - granite is a slow cooled quartz rich rock, basalt a rapidly cooled mafic rock. Basaltic lava flow, Idaho Basalt is the stuff of the ocean floor. It comes from fresh upwellings from the mantle. Basalts are extrusive igneous rocks rich in minerals containing magnesium and other similar metallic atoms. Most of these minerals have a dark color. Basalts are thus dark in color. Basalt cools rapidly as volcanic eruptions dump magma out into the air, water or inject it in little intrusions into cold rocks, crystals never have chance to grow large. A magma with at basaltic composition that cooled slowly and had a chance to grow large mineral crystals would form an intrusive igneous rock that we would call a gabbro.

86. Physical Geology Notes University of Colorado geology 1010 The basic repeat unit of a crystal or mineral is the unit cell. crystals have complex symmetries. http://ruby.colorado.edu/~smyth/G101-3.html

University of Colorado GEOLOGY 1010 Class Note 3 Minerals and Rocks A mineral is a naturally occurring homogeneous solid of definite chemical composition and ordered atomic arrangement. It is usually formed by inorganic processes. More than 5000 mineral species have been described and more than 100 new minerals are described every year. To describe a new mineral, the structure and composition must be described. Most of these 5000 minerals are rare, so that only about 200 are common enough to make up macroscopic rocks. Of these, the most abundant 50 make up 99.9% of the Earth's crust. Some examples of minerals that are familiar to you are quartz (SiO , silicon dioxide), calcite (CaCO calcium carbonate), pyrite (FeS , iron sulfide), gypsum (CaSO . 2 H O), gold (Au), silver (Ag), copper (Cu), diamond (C), graphite (C), garnet (Mg Al Si O ice (H O). Less familiar, perhaps, are apatite (Ca (PO OH) (teeth and bone), olivine (Mg SiO ) (the green mineral that makes up much of the upper mantle, gem variety: peridot), pyroxene (MgSiO ) (the other mineral in the upper mantle), muscovite (white)

87. Memphis Archaeological And Geological Society‚MAGS Newsletter Index Of Feature RockNews0103 crystals Zeolite Crystal Growth in Space RockNews0105 Diamonds Crater of Diamonds MAGS0502 minerals Crater of Diamonds State Park, AR http://www.memphisgeology.org/newsletter_index.html

The Club The Show Newsletter Youth Newsletter ... Email In order to view the MAGS Newsletter online, you must have Adobe Acrobat Reader software installed on your computer. If you do not have Reader, it is available as a free download from Adobe. Click the icon below to download reader. MAGS Rockhound News Index of Feature Articles Agates: Agate Days and Agate Ways Archaeology: 1200-Year-Old Village Found Archaeology: 5,300 Year Old Man Archaeology: Artifacts from the Pyramid of the Moon Archaeology: Clovis Points Archaeology: History in a Pot Archaeology: Napoleon's Lost Army Archaeology: NASA Deep Space 1 Probe Archaeology: Projectile Points of West Tennessee Archaeology: Pyramid of the Moon Archaeology: Sinking of the Sultana Archaeology: X-ray technology used to read inscriptions Archives: Fulton Mounds (October 1955 MAGS Article) Astronomy: The Night Sky in August

88. Oxford Brookes University - Geology - Atlas Of Ore Minerals - Gangue gangue minerals can not easily be identified in reflected light microscopy Colour colourlesswhite; Streak white; Lustre vitreous; Crystal form http://www.brookes.ac.uk/geology/8361/1999/tracey/gangue.htm

ATLAS OF COMMON ORE MINERALS Introduction Copper Minerals Lead Minerals Zinc Minerals ... Other Metallic Minerals Gangue Minerals Quiz Gangue Minerals The uses for these minerals are stated before the mineral characteristics Anhydrite/Gypsum Barite Calcite Fluorite ... Quartz gangue minerals can not easily be identified in reflected light microscopy and are better seen in transmitted light microscopy Anhydrite CaSO Gypsum CaSO O used in the construction industry Colour : colourless, white-pink-brown Streak : white Lustre : pearly-vitreous Crystal form : massive, rose, prismatic, tabular Crystal system : monoclinic Crystal hardness Cleavage : perfect Fracture : conchoidal-fibrous Feel : smooth Associated minerals : sulphur, halite, aragonite, celestine Barite BaSO used in white paint, as a protection against x-rays and as a drilling mud Colour : colourless, white, pink-brown Streak : white Lustre : pearly Crystal form : acicular-tabular Crystal system : orthorhombic Crystal hardness Cleavage : perfect Fracture : conchoidal-uneven,splintery Feel : smooth Associated minerals : calcite, fluorite, quartz, ore minerals

89. Oxford Brookes University - Geology - Atlas Of Ore Minerals - Iron Iron minerals are used in the construction industry and for alloying Colour silver grey; Streak black; Lustre metallic; Crystal form http://www.brookes.ac.uk/geology/8361/1999/tracey/iron.htm

ATLAS OF COMMON ORE MINERALS Introduction Copper Minerals Lead Minerals Zinc Minerals Iron Minerals Other Metallic Minerals Gangue Minerals Quiz Iron Minerals Iron minerals are used in the construction industry and for alloying Arsenopyrite Hematite Magnetite Pyrite ... Pyrrhotite Arsenopyite FeAsS Colour : silver grey Streak : black Lustre : metallic Crystal form : massive-acicular Crystal system : orthorhombic Crystal hardness Cleavage : parallel to faces of prism Fracture : uneven Smell : similar to garlic on freshly broken surfaces Associated minerals : stibnite, galena, pyrite Colour : white-light grey Birefringence/pleochroism : weak-yellowish XPL anisotropy : moderate-strong Internal reflections : none Textures : zoning Reflectivity : moderate Hardness : very hard Hematite Fe O Colour : black with red tinge Streak : red-brown Lustre : metallic-dull Crystal form : reniform-massive-tabular-rose Crystal system : trigonal Crystal hardness Cleavage : none Fracture : conchoidal Associated minerals : siderite, limonite, magnetite, pyrite, quartz Colour : grey-white Birefringence/pleochroism : weak XPL anisotropy : distinct Internal reflections : deep red Textures : lamellar Reflectivity : low Hardness : very hard Magnetite Fe O Colour : dark grey-black Streak : black Lustre : metallic-dull Crystal form : tabular-massive Crystal system : cubic Crystal hardness Cleavage : imperfect Fracture : uneven Associated minerals : ilmenite, apatite, augite, hematite, amphiboles

90. Maine Geology - May Site Of The Month Geologic Site of the Month May 1998. Mineral Collecting in Maine - 1998 Update Figure 3 shows one of the giant andalusite crystals that were found in http://www.state.me.us/doc/nrimc/mgs/sites-1998/may98.htm

Skip Maine state header navigation Agencies Online Services Web Policies ... Help State Search: MAINE DEPARTMENT OF CONSERVATION Maine Geological Survey Geologic Site of the Month - May 1998 Mineral Collecting in Maine - 1998 Update INTRODUCTION Mineral collecting ("rockhounding") continues to be a very popular hobby in Maine. This state is world famous for the gems and rare minerals that have been found here. Tourmaline, aquamarine beryl, garnet, and amethyst are among the more desirable minerals occurring in veins of coarse-grained granite called "pegmatite." Earlier in this century pegmatite rocks in Oxford, Androscoggin, and Sagadahoc Counties were extensively mined for feldspar and mica. Gem crystals with obvious value were usually saved during these operations, but other interesting minerals were thrown onto the "dumps" of waste rock. Collectors have dug through the dump piles ever since, finding specimens for their collections. Mineral collecting has many positive aspects. It is a low-cost hobby that is ideal for people who want to combine outdoor recreation with the fun of a treasure hunt. The arranging and study of a well-labeled mineral collection can also be an enjoyable and educational activity throughout the year. Some families plan their Maine vacations around a series of day trips to collecting sites. Gold panning is a special type of mineral pursuit that has its own dedicated followers. The East Branch of the Swift River in Byron is the most popular stream for gold seekers and has yielded some big nuggets (Figure 1), but many other Maine rivers probably contain traces of gold in their gravelly sediments.

91. Northwest Geological Society : Calendar Far out fossils, minerals and crystals A family adventure; Alberta August 811 Geological Society of America AND Geological Association of http://www.scn.org/nwgs/joust/calendar.htm

Menu Pacific Northwest Region GeoScience Calendar Please query links or contacts of non-NWGS events to confirm information before attending events. We are not notified of program changes or errors for some functions, and thus are not responsible for calendar inaccuracies related to non-NWGS listings. This web page is updated periodically. Contact: Dave Knoblach Location Key WA Washington, OR Oregon, BC British Columbia, ID Idaho, MT Montana, CA California, Other Other Locations (select functions only) Event Symbols Lecture: Field Trip: Conference: Recurring GeoScience Functions July, 2005 WA July 17- 23: Geological Society of AmericaField Forum Mt. St. Helens (For teachers) WA July 18 - 22: Northwest Natural Resources Institute Natural Resources Teacher Workshop OR July 23: Geological Society of the Oregon Country ): Pat Pringle (Washington Division of Geology and Earth Resources), Mt. St. Helens WA July 27 - 31: North Cascades Institute : Art Kruckeberg, Chris Morgan, Jon Riedel, and Rainer Stahlberg, North Cascades Naturalists Retreat: Glaciers, Rivers, Rare Plants and Wildlife

92. Bob's Rock Shop: Books About Rocks And Minerals Hundreds of minerals are descrived, with details such as geologic distribution, Rocks, minerals, Gems, crystals, Fossils is a sure to be appreciated http://www.rockhounds.com/rockshop/books/minerals.shtml

Bead Work Buyer's Guides Casting Chain Making ... Wire Work References for Rockhounds Rocks and Minerals Order This Book 1000 Photos of Minerals and Fossils by Alain Eid Order This Book Amber Window to the Past by David A. Grimalsi The unique properties of amber (fossilized tree resin) have long intrigued many people and never more so than now, in the wake of Michael Chriton's fictional Jurassic Park and real scientific breakthroughs in achieving what Chriton theorized: the cloning of an ancient DNA sequence of amber. Originally published to accompany the hugely popular 1996 exhibition organized by the American Museum of Natural History in New York, Amber: Window to the Past explores thoroughly the various aspects of this remarkable material, from its part in delineating evolutionary history, through the study of folklore surrounding it, to is use in decorative arts and jewelry. The 230 gorgeous and amazingly varied photographs and drawings, 115 in color and never before published, vividly illuminate the roles of amber in both nature and art. This engrossing and readable book will delight lovers of science, history and art as well as anyone intrigued by stories of how we and our world have evolved. Soft cover, 9" x 11", 216 pages. Order This Book The Encyclopedia of Gemstones and Minerals by Martin Holden Lavishly illustrated with over 400 color photographs and illustrations

93. Geology 111G/Lecture 3 geology 111G/ 1/14/2005. Lecture 4. minerals. Definition. Properties A. Crystal structure is characteristic of a specific mineral. http://www.nmsu.edu/~geology/lawton/Lec4minerals.html

Geology 111G/ Lecture 4. Minerals Definition Properties Rock-forming minerals Rocks I. Mineral Naturally occurring, solid crystalline substance, generally inorganic, with a specific chemical composition. A. Crystal structure is characteristic of a specific mineral. B. Chemical composition may vary within limits. C. Minerals form by crystallization , which is crystalline assembly of atoms in a gas or liquid. This may take place during cooling of a hot melt or by precipitation from a concentrated solution. II. Mineral properties Physical properties of minerals determined by internal arrangement of atoms, chemical formula and bond types. A. Crystal habit Shape of a crystal is determined by atomic structure. The atomic structure repeats itself throughout the mineral; this is the crystal lattice Crystal faces are the planar surfaces that develop during crystal growth. Cubic habit of halite (NaCl) is determined by the equally spaced disposition of sodium and chlorine ions in the crystal lattice. B. Polymorphs Different crystal structures with the same chemical composition. The classic example is carbon.

94. PtyS/LPL Laserdisc Collection: Geology And Meteorology Mineral Properties Bowen s reaction series Crystal forms Crystal lattice diagrams minerals in thin section Hardness Cleavage Streak Luster Fracture Tenacity http://www.lpl.arizona.edu/resources/visuals/geology_disc.html

Department of Planetary Sciences Lunar and Planetary Laboratory Resources Planetary Sciences Laserdisc Collection: Geology and Meteorology All Laserdiscs are stored in the podium. Please return after use and lock them up! Earth Science - Geology and Meteorology ODC Living Textbook Series (The catalog listing the still frames and movie clips is in the podium.) Introduction and Credits Side One/Side Two Directory Plate Tectonics Geologic Time Scale Diagrams Computer generated image of Earth topography Earth's Atmosphere Diagrams Cloud catalog Meteorology from space Ground weather Nimbus GOES weather patrol GOES views of Hurricane Allen Aurorae Ground observations Aurora Borealis Aurora Australis Mt. St. Helens USGS archives May 18, 1980 Ash cloud Hawaiian Volcanoes Hawaiin Volcanoes Nat'l Park HVO superset Volcanoes of the World North America Iceland International The African Rift Valley Yellowstone Nat'l Park Earthquakes Diagrams North American earthquakes Earthquake lights Glacial processes Glaciers Glacial erosion Glacial surfaces Glacial termini Moraines Glacial lakes Glacial outwash Glacial ice Ice rafting Icebergs Fluvial processes Weathering and erosion General fluvial processes Ripple marks Braided streams Meanders and oxbows Drainage patterns Flooding Falls Dams

95. PSIgate - Physical Sciences Information Gateway Search/Browse Results The site also provides images of mostly uncommon minerals, and links to other Educational material Crystal Chemistry Lecture 5 geology 311 Earth http://www.psigate.ac.uk/roads/cgi-bin/psibrowse.pl?toplevel=earth&limit=0&subje

96. UWRF Geology - Dr. Bill Cordua Why do pyrite crystals show different faces Moganite a common mineral Minnesota Twin crystals Moonstone - An exsolution to its mystery geology and http://www.uwrf.edu/~wc01/leaverite.html

LEAVERITE NEWS ARTICLES BY WILLIAM S. CORDUA These are one-page popular science articles written on mineralogical and geological subjects for the Leaverite News newsletter of the St. Croix Rockhounds. They have been reprinted by other newsletters. Some have won regional and national awards through the Midwest Federation and American Federation. Copies of those not linked yet from this page can be obtained from me. E-MAIL ** indicates award-winning articles What are those fibers in my rose quartz? Pieces of eight minerals Cave spar Disorderly opal ... Floating Copper The Great St. Croix Meteorite Hunt 1997 Wisconsin Wavellite **Minerals from Kidney Stones Agates - Full of Fiber Rust Minerals ... Mellen Black Granite A mineral from giant red suns A Lake Full of Lead Blue, Blue, My Quartz is Blue Why do pyrite crystals show different faces Moganite - a common mineral with a disapproved name Book review : Gene LaBerge, Geology of Lake Superior Epidote Hibbingite - swimming pool mineral A new place to look for diamonds Hourglass gypsum Wisconsin talc Geology and the Growth of Downtown Stillwater Moon minerals found on earth Moonmilk The fire of opal 1992 A St. Croix Meteorite

97. BC Education - Geology 12 - Earth Materials (Minerals) geology 12 Earth Materials (minerals). This sub-organizer contains the Have students describe, sketch, or make models of simple crystal shapes (eg, http://www.bced.gov.bc.ca/irp/esg/12earmin.htm

Geology 12 - Earth Materials (Minerals) This sub-organizer contains the following sections: Prescribed Learning Outcomes Suggested Instructional Strategies Suggested Assessment Strategies Recommended Learning Resources PRESCRIBED LEARNING OUTCOMES It is expected that students will: outline the importance and abundance of various elements in the earth's crust demonstrate an ability to use the following properties in identifying minerals: simple crystal shape cleavage fracture hardness specific gravity (relative density) colour streak lustre special properties, such as reaction to dilute HCl magnetism use appropriate references and tests to describe and identify the following minerals: silicates and aluminosilicates: quartz and varieties of quartz potassium feldspar and plagioclase feldspar muscovite, biotite, and talc augite (pyroxene) and hornblende (amphibole) garnet asbestos olivine oxides: hematite, limonite, magnetite sulphides: pyrite, chalcopyrite, galena, sphalerite, molybdenite, bornite carbonates and sulphates: calcite, malachite, azurite, gypsum

98. Gems Minerals Bibliography minerals, crystals, and Gems Stepping Stones to Inquiry The Care and Conservation of Geological Material minerals, Rocks, Meteorites, and Lunar Finds. http://www.calacademy.org/research/library/naturalist_center/biblio/gems.htm

California Academy of Sciences Library World Wide Web Books Children's Books Video WORLD WIDE WEB Chemical Compositions of Minerals and Gems http://www.geology.wisc.edu/~jill/mineral.html It’s just like the title sounds. Desert Environment: Minerals and Geology Index http://www.desertusa.com/Thingstodo/geo/geology.html Click on a mineral to find more information. Gemology http://www.geocities.com/Y o semite/trails/3085/Gemmology.htm Links, links, and more links about gemology, the study of gems. Gems and Precious Stones http://www.geology.wisc.edu/~jill/306.html Many images and resources. GeoGem: Gemology Overview http://www.geogem.com/gemmology.htm Very useful information on the gemological properties of gem stones. The Image http://www.theimage.com/ Pictures of minerals and gemstones. The Mineral Gallery http://www.themineralgallery.com/ Descriptions, pictures and information on gemstones and minerals, by name, class, groupings and physical properties. Mineralogy Database http://www.webmineral.com/

99. Glossary Of Selected Terms minerals not bounded by crystal faces. Metamorphism (geological)..Changes in rocks brought about by heat and pressure acting in the rocks just below the http://ist-socrates.berkeley.edu/~eps2/wisc/glossary.html

Glossary of Selected Terms (An index is also available Absorption Spectrum ....Colors of light least absorbed combining to produce the color of the stone. The stone, when viewed by spectroscope, will show as dark bands in characteristic positions the colors most strongly absorbed. Acicular...Needlelike; refers to the growth of a mineral in long and slender crystals. Adamantine... Very high luster. Aggregate...Intergrowth of several crystals, these may be globular, fibrous, reniform, or radiating fibrous. Adularescence...The sheen of color seen in moonstone and other feldspars of the adularia variety. Allochromatic Minerals...Minerals that are colorless when pure, the color coming from coloring agents, most of which are, cobalt, copper, chromium, titanium, vanadium, manganese, and iron. Examples of this are beryl,corundum, quartz, and spinel. Alluvium...Continental sediments due to transport and deposition of gravel, sand, and clay by running water, rivers, and streams. (See alluvial Alpha rays...Helium atoms with double positive charge.

100. Memphis Archaeological And Geological Society‚Lapidary Arts: The Color Of Cryst 06.21.00The color of a crystal can be its most striking feature. The causes of color are varied, and many minerals occur in a range of colors. http://www.memphisgeology.org/l_color.html

The Club The Show Newsletter Archaeology ... Email LAPIDARY ARTICLES Color of Crystals Sawing Gemstones A Visit to the Mineral and Lapidary Museum of Henderson County, NC The Color of Crystals Idiochromatic: Some minerals are nearly always the same color because certain light-absorbing atoms are an essential part of their crystal structure. These minerals are described as idiochromatic. For example, copper minerals are nearly always red, green or blue according to the nature of the copper present.: Allochromatic: A large number of minerals occur in a wide range of colors caused by impurities or light-absorbing defects in the atomic structure. For example, quartz, diamond, beryl, and corundum can be red, green, yellow, and blue. These minerals are described as allochromatic. Play of colors: The color os some minerals is really a play of colors like that seen in an oil slick or a soap bubble. This may be produced when the light is affected by the physical structure of the crystals, such as twinning or cleavage planes, or by the development duirng growth of thin films. Microscopic "intergrowths" of plate-like inclusions also interfere with the light.

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