Geology of Buffalo Bill State Park
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JadeWyoming State State Mineral & Gem News Society, Inc. Award-Winning WSMGS Website: wsmgs.org Volume 2020, Issue # 2 The Color of Minerals By Stan Strike RMFMS WY State Director When I look at a mineral, the first thing I usually notice is its color. But why are some minerals always the same color — such as gold and azurite — while other minerals can be different colors, such as quartz and fluorite? The answer to this question requires a brief review of why we see color, and why rock hounds should not rely solely on color to identify minerals. Why We See Color WSMGS OFFICERS White light, such as sunlight, contains all the primary colors of the visible President: Jim Gray spectrum: red, orange, yellow, green, blue, indigo and violet (often shortened [email protected] to the acronym ROYGBIV, or ROY G. BIV). The colors making up visible light each have specific wavelengths of energy, Vice President: Linda Richendifer [email protected] but combined we see visible light, but when separated, we may see a rainbow: ROYGBIV. Secretary: Leane Gray Red has the longest wavelength, with the least energy, and violet has the [email protected] shortest wavelength, with more energy. When light passes through water droplets, it separates according to how much energy each color has. The Treasurer: Stan Strike wavelengths of color having the least energy are bent, or refracted, the most. [email protected] Violet, having the shortest wavelengths, is refracted (bent) the least. There- Historian: Roger McMannis fore, when you see a rainbow, red is always on the top and violet on the un- [email protected] derside. (Continued on Page 2) Jade State News Editor: Ilene Olson State/regional rock show still planned [email protected] for June 19-21. See pages 6-7 and 22-23 RMFMS State Director: Table of Contents Stan Strike [email protected] The Color of Minerals.................Page 1 Wet Polishing Guide............Page 14 State Rock Show Flyer ..............Page 6 WSMGS Board Meeting.......Page 15 RMFMS WY PLAC Director: State Rock Show is happening Page 7 Club News............................Page 19 Rich Gerow Rock Cycle Cartoon..................Page 10 Upcoming Rock Shows.......Page 22 [email protected] Making Geological Maps Easier to View....................................................Page 7 Rockhounding on Facebook.......................................................................Page 8 The WSMGS conducts Geology of Buffalo Bill State Park............................................................Page 11 meetings quarterly and List of Lodging in & near Big Piney/Marbleton, Wyoming.....................Page 23 as special events require. WSMGS Rock Club List ............................................................................Page 24 Volume 2020 Jade State News Issue #2#1 Colors of Minerals (Continued from Page 1) The color of an object we see is dependent upon what light wavelengths are absorbed by the object, and what combination of wavelengths of light are reflected back to our eyes. The wavelength of light that is most strongly reflected or scattered is what gives an object its visible color, because this is the one that most clearly reaches our eyes. Minerals are made up of elements, and each element has a specific property as to absorbing and reflecting light. The same element can create different colors, depending on how much energy is present within each mineral as it is formed. The primary elements that absorb visible-spectrum color are the transition metals on the Periodic Table. The most familiar of the 38 transition metals are iron (red, green, yellow); cobalt (blue); and nickel (green). Others in- clude vanadium (red, orange); manganese (red); chromium (red, green); gold (yellow); titanium (blue); and copper (green, blue). Some rare-earth elements also create color through their absorption patterns, including scandium, yttrium, lanthanum, and cerium. The combination of elements making up minerals creates the rainbow of different colors that we see. Two classes of minerals: Idochromatic and Allochromatic Idichromatic Minerals These minerals always have the same color because of the presence of the same combination of elements in the mineras’ chemical formula . These minerals always absorb certain wavelengths of light and reflect the same combi- nation of wavelengths of color that we see. Examples: • Gold (Au) is yellow, because the element absorbs all other colors except yellow. • Azurite is blue, because the copper in azurite molecules absorbs all other colors except blue. • Crocoite is red-orange, because the chromium in crocoite molecules absorbs all the other colors. Photos courtesy of Treasure Mountain Mining (Continued on Page 3) Page 2 Volume 2020 Jade State News Issue #2#1 Colors of Minerals (Continued from Page 2) Allochromatic Minerals • Citrine: Inclusions of iron (Fe+++) cause the yellow color in citrine. These minerals would be colorless in their pure form, • Rose Quartz: Trace amounts of titanium or manga- but they contain additional elements that create dif- nese turn quartz pink. ferent visible colors. To greatly simplify, there are four • Green fluorite: X-Ray diffraction tests of fluorite causes of color in allochromatic minerals: impurities, from the William Wise Mine in New Hampshire showed inclusions, charge transfer and color centers. that the element yttrium, a known coloring agent, con- stituted 0.2 percent of the sample. Impurities • Aquamarine: Inclusions of iron (Fe++) are respon- Tiny amounts — as little as one-tenth of 1 percent — of sible for the blue color in beryl. an impurity in the molecular structure of a mineral can • Heliodor: Iron (Fe+++) in beryl's molecular struc- determine that mineral's color. The amount and type of ture turns it yellow. impurities affect the color of the mineral. •Morganite: Manganese as Mn++ turns morganite Examples: pink. • Amethyst: Add some iron to clear, pure quartz and •Red beryl: The red color is caused by Manganese it becomes purple. (Mn+++). Photos courtesy of Treasure Mountain Mining (Continued on Page 4) Page 3 Volume 2020 Jade State News Issue #2#1 Colors of Minerals (Continued from Page 3) Inclusions to turn green. Inclusions of a second mineral, or even air, within a • Jasper: Hematite inclusions can turn jasper red. host mineral also can alter a mineral's color. • Milky quartz: Inclusions of very small air bubbles in Examples: clear quartz turn it white, in which case it is called milky • Prase quartz: Hedenbergite inclusions in quartz give quartz. prase its green color. • Rutilated Quartz: Rutile inclusions in quartz give it • Green quartz: Chlorite inclusions in quartz cause it a golden hue. Photos courtesy of Treasure Mountain Mining Charge Transfer red spectrum to be absorbed, producing the deep blue When two or more elements in a mineral exchange color sapphires. electrons, this is called charge transfer. The movement of • Aquamarine: Small amounts of iron in valence electrons results in states (Fe++ and selective absorption Fe+++) cause an of light. electron transfer that absorbs red Examples: light, resulting in • Sapphires con- the color blue. tain small amounts • Tourma- of titanium (Ti) line: Manganese and iron (Fe). The (Mn++) and ti- electron transfer be- tanium (Ti4+) tween titanium and swap electrons, iron causes light in creating a yel- the yellow through low-green color. Photos courtesy of Treasure Mountain Mining (Continued on Page 5) State/regional rock show still planned for June 19-21. See pages 6-7 and 23 for details. Page 4 Volume 2020 Jade State News Issue #2#1 Colors of Minerals (Continued from Page 4) Color Centers tain wavelengths of light, and the colors reflected (not A color center is a defect in the molecular structure absorbed) are seen as the mineral's color. of a mineral. The defect is often due to damage from Examples: heating or natural radiation. UV light (from prolonged • Purple fluorite: When a negative ion is missing from exposure to sunlight, the structure (sometimes for example) can also referred to as a Frenkel cause color change. defect), it creates a site Color centers can that attracts and traps a be removed by add- free electron. The trapped ing energy, as is some- electron creates an elec- times done by heating tron color center, which is gemstones to change responsible for the color in their color. There purple fluorite. are two types of col- • Smoky quartz: Radi- or-center defects: Photos courtesy of Treasure Mountain Mining ation, either natural or • An unattached excess electron in the atoms making man-made, creates a hole in the silicon dioxide mole- up an element can be trapped in a empty space in the cule, which changes colorless quartz to smoky quartz. mineral's chemical structure. • Topaz: The color in natural yellow, orange or brown • A missing electron in the atoms making up an ele- topaz results from a color center that is stable to light. If ment creates a change in the mineral’s chemical formula. colorless topaz is irradiated, it creates a hole in the color In both cases, the flaws result in the absorption of cer- center, making it yellow, orange, brown or blue. Enhancing the Color of Minerals That Contain Transition Elements Understanding how Mother Nature produces and very expensive and no one could easily tell that the ir- changes the colors of minerals, man has learned to use radiated blue gems were not natural and was being sold methods that cause electrons to transition or move as “blue ice” topaz. The problem was, the dealer was not within the atoms making up certain kinds of elements telling customers the topaz had been irradiated. (transition elements). Adding extra man-made energy to By using man-made energy sources to treat minerals these elements enhances or changes the natural colors containing transition elements, rock hounds have been of these minerals so that the color “imitates” rarer and able to produce intense and altered mineral colors. It more expensive minerals. is now general practice by reputable mineral dealers to Example 1: Since 1950, almost all natural prasiolite disclose any treatment affecting mineral color.