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Lustre (mineralogy)
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<h2 id="common-terms">Common terms</h2> <h3>Adamantine lustre</h3> <p>Adamantine minerals possess a superlative lustre, which is most notably seen in <a href="/facts/Diamond/IBUdnd1y">diamond</a>.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> Such minerals are transparent or translucent, and have a high <a href="/facts/Refractive_index/yjkzvgeE">refractive index</a> (of 1.9 or more).<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> Minerals with a true adamantine lustre are uncommon, with examples including <a href="/facts/Cerussite/zutKQG6A">cerussite</a>, <a href="/facts/Zircon/84APfbLt">zircon</a>, and <a href="/facts/Cubic_zirconia/zaxk0fuh">cubic zirconia</a>.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p><p>Minerals with a lesser (but still relatively high) degree of lustre are referred to as subadamantine, with some examples being <a href="/facts/Garnet/kqh2lWQI">garnet</a> and <a href="/facts/Corundum/B7RRbcaE">corundum</a>.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <h3>Dull lustre</h3> <p>Dull (or earthy) minerals exhibit little to no lustre, due to coarse granulations which scatter light in all directions, approximating a <a href="/facts/Lambertian_reflectance/gyNfTmph">Lambertian reflector</a>. An example is <a href="/facts/Kaolinite/N7D6K65q">kaolinite</a>.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> A distinction is sometimes drawn between dull minerals and earthy minerals,<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> with the latter being coarser, and having even less lustre. </p> <h3>Greasy lustre</h3> <p>Greasy minerals resemble fat or grease. A greasy lustre often occurs in minerals containing a great abundance of microscopic inclusions, with examples including <a href="/facts/Opal/LF7Xa7nK">opal</a> and <a href="/facts/Cordierite/4kSrwpuA">cordierite</a>, <a href="/facts/Jadeite/VGgFqkgJ">jadeite</a>.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> Many minerals with a greasy lustre also feel greasy to the touch.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> <h3>Metallic lustre</h3> <p>Metallic (or splendent) minerals have the lustre of polished metal, and with <a href="/facts/Ideal_surface/cjWao4Pl">ideal surfaces</a> will work as a <a href="/facts/Reflection_(physics)/BhcjDs79">reflective surface</a>. Examples include <a href="/facts/Galena/eSaK62FA">galena</a>,<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> <a href="/facts/Pyrite/41CYREyr">pyrite</a><a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> and <a href="/facts/Magnetite/SVxoGUs2">magnetite</a>.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p> <h3>Pearly lustre</h3> <p>Pearly minerals consist of thin transparent co-planar sheets. Light reflecting from these layers gives them a lustre reminiscent of <a href="/facts/Pearl/7ombxKgg">pearls</a>.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> Such minerals possess perfect <a href="/facts/Cleavage_(crystal)/p4YHe01X">cleavage</a>, with examples including <a href="/facts/Muscovite/jMq51dyg">muscovite</a> and <a href="/facts/Stilbite/ccu8dF1x">stilbite</a>.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> </p> <h3>Resinous lustre</h3> <p>Resinous minerals have the appearance of <a href="/facts/Resin/r1uVThQ8">resin</a>, <a href="/facts/Chewing_gum/S48CIm9D">chewing gum</a> or (smooth-surfaced) plastic. A principal example is <a href="/facts/Amber/GHP6h5gx">amber</a>, which is a form of fossilized resin.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p> <h3>Silky lustre</h3> <p>Silky minerals have a parallel arrangement of extremely fine fibres,<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> giving them a lustre reminiscent of <a href="/facts/Silk/XhxPpvvS">silk</a>. Examples include <a href="/facts/Asbestos/dEnjQyee">asbestos</a>, <a href="/facts/Ulexite/bejMrcy6">ulexite</a> and the <a href="/facts/Satin_spar/ChMIJw4P">satin spar</a> variety of <a href="/facts/Gypsum/MItYU70n">gypsum</a>. A fibrous lustre is similar, but has a coarser texture. </p> <h3>Submetallic lustre</h3> <p>Submetallic minerals have similar lustre to metal, but are duller and less reflective. A submetallic lustre often occurs in near-opaque minerals with very high refractive indices,<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> such as <a href="/facts/Sphalerite/5NumvnzR">sphalerite</a>, <a href="/facts/Cinnabar/MUzsHjFw">cinnabar</a>, <a href="/facts/Anthracite/xYt8pIGe">anthracite</a>, and <a href="/facts/Cuprite/WdFFUXo2">cuprite</a>. </p> <h3>Vitreous lustre</h3> <p>Vitreous minerals have the lustre of <a href="/facts/Glass/hezRsAGf">glass</a>. (The term is derived from the Latin for glass, <i>vitrum</i>.) This type of lustre is one of the most commonly seen,<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> and occurs in transparent or translucent minerals with relatively low refractive indices.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> Common examples include <a href="/facts/Calcite/gKMHYQJo">calcite</a>, <a href="/facts/Quartz/4n86tE2G">quartz</a>, <a href="/facts/Topaz/jjgWXsSv">topaz</a>, <a href="/facts/Beryl/Fl7q1Hl9">beryl</a>, <a href="/facts/Tourmaline/6nbcGRyu">tourmaline</a> and <a href="/facts/Fluorite/y2G7C8zk">fluorite</a>, among others. </p> <h3>Waxy lustre</h3> <p>Waxy minerals have a lustre resembling <a href="/facts/Wax/MAXhjzNh">wax</a>. Examples include <a href="/facts/Jade/s9HpCT81">jade</a><a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> and <a href="/facts/Chalcedony/46xQNNxs">chalcedony</a>.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> </p> <h2 id="optical-phenomena">Optical phenomena</h2> <h3>Asterism</h3> <p><a href="/facts/Asterism_(gemmology)/cwabWRS6">Asterism</a> is the display of a star-shaped luminous area. It is seen in some <a href="/facts/Sapphire/C11GJAmm">sapphires</a> and <a href="/facts/Ruby/faGnqzW8">rubies</a>, where it is caused by impurities of <a href="/facts/Rutile/qwJH5ElN">rutile</a>.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a><a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> It can also occur in <a href="/facts/Garnet/kqh2lWQI">garnet</a>, <a href="/facts/Diopside/vyRkJB2W">diopside</a> and <a href="/facts/Spinel/Nb7K5ctV">spinel</a>. </p> <h3>Aventurescence</h3> <p><a href="/facts/Aventurescence/QN9apf4N">Aventurescence</a> (or aventurization) is a reflectance effect like that of <a href="/facts/Glitter/92J5LqBl">glitter</a>. It arises from minute, preferentially oriented mineral platelets within the material. These platelets are so numerous that they also influence the material's body colour. In <a href="/facts/Aventurine/edxX8SV2">aventurine quartz</a>, chrome-bearing <a href="/facts/Fuchsite/04ADHdJS">fuchsite</a> makes for a green stone and various <a href="/facts/Iron_oxide/KDo8hLWn">iron oxides</a> make for a red stone.<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> </p> <h3>Chatoyancy</h3> <p><a href="/facts/Chatoyancy/jpeyA5kk">Chatoyant</a> minerals display luminous bands, which appear to move as the specimen is rotated. Such minerals are composed of parallel fibers (or contain fibrous voids or inclusions), which reflect light into a direction perpendicular to their orientation, thus forming narrow bands of light. The most famous examples are <a href="/facts/Tiger%27s_eye/EG7PRPtq">tiger's eye</a> and <a href="/facts/Chrysoberyl/RRDtRWJE">cymophane</a>, but the effect may also occur in other minerals such as <a href="/facts/Beryl/Fl7q1Hl9">aquamarine</a>, <a href="/facts/Moonstone_(gemstone)/XN5wP0E7">moonstone</a> and <a href="/facts/Tourmaline/6nbcGRyu">tourmaline</a>. </p> <h3>Colour change</h3> <p>Colour change is most commonly found in alexandrite, a variety of <a href="/facts/Chrysoberyl/RRDtRWJE">chrysoberyl</a> gemstones. Other gems also occur in colour-change varieties, including (but not limited to) <a href="/facts/Sapphire/C11GJAmm">sapphire</a>, <a href="/facts/Garnet/kqh2lWQI">garnet</a>, <a href="/facts/Spinel/Nb7K5ctV">spinel</a>. Alexandrite displays a colour change dependent upon light, along with strong <a href="/facts/Pleochroism/EJJclyzk">pleochroism</a>. The gem results from small-scale replacement of aluminium by chromium oxide, which is responsible for alexandrite's characteristic green to red colour change. Alexandrite from the <a href="/facts/Ural_Mountains/gzNoPkt6">Ural Mountains</a> in Russia is green by daylight and red by incandescent light. Other varieties of alexandrite may be yellowish or pink in daylight and a columbine or raspberry red by incandescent light. The optimum or "ideal" colour change would be fine emerald green to fine purplish red, but this is rare. </p> <h3>Iridescence</h3> <p>Iridescence is the 'play' or 'fire' of rainbow-coloured light caused by very thin regular structures or layers beneath the surface of a gemstone. Similar to a thin film of oil on water, these layers interfere with the rays of reflected light, reinforcing some colours and cancelling others. Iridescence is seen at its best in precious <a href="/facts/Opal/LF7Xa7nK">opal</a>.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a></p> <h3>Schiller</h3> <p>Schiller (German, literally "shimmer"), is the metallic <a href="/facts/Iridescence/ykc1opK8">iridescence</a> originating from below the surface of a stone that occurs when light is reflected between layers of minerals. It is seen in <a href="/facts/Moonstone_(gemstone)/XN5wP0E7">moonstone</a> and <a href="/facts/Labradorite/PyDfR62q">labradorite</a> and is very similar to <a href="/facts/Adularescence/34tvK8up">adularescence</a> and <a href="/facts/Aventurescence/QN9apf4N">aventurescence</a>.<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> </p> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>GIA Gem Reference Guide. Gemological Institute of America. 1995. ISBN 0-87311-019-6. <a href="0-87311-019-6" target="_blank">0-87311-019-6</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Duda, Rudolf & Rejl, Lubos (1990). Minerals of the World. Arch Cape Press. ISBN 0-517-68030-0. <a href="0-517-68030-0" target="_blank">0-517-68030-0</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Duda, Rudolf & Rejl, Lubos (1990). Minerals of the World. Arch Cape Press. ISBN 0-517-68030-0. <a href="0-517-68030-0" target="_blank">0-517-68030-0</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>GIA Gem Reference Guide. Gemological Institute of America. 1995. ISBN 0-87311-019-6. <a href="0-87311-019-6" target="_blank">0-87311-019-6</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"Webmineral: Kaolinite Mineral Data". Retrieved 2008-06-21. <a href="http://www.webmineral.com/data/Kaolinite.shtml" target="_blank">http://www.webmineral.com/data/Kaolinite.shtml</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Hankin, Rosie (1998). Rocks, Crystals & Minerals. Quintet Publishing. ISBN 1-86155-480-X. <a href="1-86155-480-X" target="_blank">1-86155-480-X</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Duda, Rudolf & Rejl, Lubos (1990). Minerals of the World. Arch Cape Press. ISBN 0-517-68030-0. <a href="0-517-68030-0" target="_blank">0-517-68030-0</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"Emporia State University: GO 340 Gemstones & Gemology: Visual Properties". Archived from the original on 2011-06-12. Retrieved 2008-06-19. <a href="https://web.archive.org/web/20110612080930/http://www.emporia.edu/earthsci/amber/go340/visual.htm" target="_blank">https://web.archive.org/web/20110612080930/http://www.emporia.edu/earthsci/amber/go340/visual.htm</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>"Webmineral: Galena Mineral Data". Retrieved 2008-07-05. <a href="http://webmineral.com/data/Galena.shtml" target="_blank">http://webmineral.com/data/Galena.shtml</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"Webmineral: Pyrite Mineral Data". Retrieved 2008-07-05. <a href="http://webmineral.com/data/Pyrite.shtml" target="_blank">http://webmineral.com/data/Pyrite.shtml</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>"Webmineral: Magnetite Mineral Data". Retrieved 2008-07-05. <a href="http://webmineral.com/data/Magnetite.shtml" target="_blank">http://webmineral.com/data/Magnetite.shtml</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>"Optical properties of Rocks and Minerals". Retrieved 2008-06-01. <a href="http://www.rockcollector.co.uk/opticalprop.htm" target="_blank">http://www.rockcollector.co.uk/opticalprop.htm</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Duda, Rudolf & Rejl, Lubos (1990). Minerals of the World. Arch Cape Press. ISBN 0-517-68030-0. <a href="0-517-68030-0" target="_blank">0-517-68030-0</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>"Webmineral: Amber Mineral Data". Retrieved 2008-06-21. <a href="http://webmineral.com/data/Amber.shtml" target="_blank">http://webmineral.com/data/Amber.shtml</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Duda, Rudolf & Rejl, Lubos (1990). Minerals of the World. Arch Cape Press. ISBN 0-517-68030-0. <a href="0-517-68030-0" target="_blank">0-517-68030-0</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Duda, Rudolf & Rejl, Lubos (1990). Minerals of the World. Arch Cape Press. ISBN 0-517-68030-0. <a href="0-517-68030-0" target="_blank">0-517-68030-0</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>"Optical properties of Rocks and Minerals". Retrieved 2008-06-01. <a href="http://www.rockcollector.co.uk/opticalprop.htm" target="_blank">http://www.rockcollector.co.uk/opticalprop.htm</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>Duda, Rudolf & Rejl, Lubos (1990). Minerals of the World. Arch Cape Press. ISBN 0-517-68030-0. <a href="0-517-68030-0" target="_blank">0-517-68030-0</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>"Emporia State University: GO 340 Gemstones & Gemology: Jade". Archived from the original on 2011-06-12. Retrieved 2008-07-14. <a href="https://web.archive.org/web/20110612081228/http://www.emporia.edu/earthsci/amber/go340/jade.htm" target="_blank">https://web.archive.org/web/20110612081228/http://www.emporia.edu/earthsci/amber/go340/jade.htm</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Bonewitz, Ronald Louis (2005). Rock and Gem. Dorling Kindersley. pp. 152–153. ISBN 0-7513-4400-1. <a href="0-7513-4400-1" target="_blank">0-7513-4400-1</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>Bonewitz, Ronald Louis (2005). Rock and Gem. Dorling Kindersley. pp. 152–153. ISBN 0-7513-4400-1. <a href="0-7513-4400-1" target="_blank">0-7513-4400-1</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> <li id="fn:22"><p>Emsley, John (2001). Nature's Building Blocks: An A-Z Guide to the Elements. Oxford University Press. pp. 451–53. ISBN 0-19-850341-5. <a href="0-19-850341-5" target="_blank">0-19-850341-5</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></p></li> <li id="fn:23"><p>Bonewitz, Ronald Louis (2005). Rock and Gem. Dorling Kindersley. pp. 152–153. ISBN 0-7513-4400-1. <a href="0-7513-4400-1" target="_blank">0-7513-4400-1</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></p></li> <li id="fn:24"><p>G., Read, Peter (2008). Gemmology (3rd ed.). London: N.A.G. ISBN 9780719803611. OCLC 226280870.{{cite book}}: CS1 maint: multiple names: authors list (link) <a href="9780719803611" target="_blank">9780719803611</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></p></li> <li id="fn:25"><p>Shipley, Robert M. (2007). Dictionary of gems and gemology. Read Books. p. 93. ISBN 978-0-87311-007-5. <a href="978-0-87311-007-5" target="_blank">978-0-87311-007-5</a> <a href="#fnref:25" class="footnote-back-ref">↩</a></p></li> </ol>