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MINERAL PROPERTIES and identification procedures TRANSPARENCY
The amount of light passed through a mineral determines its transparency. Most light passes through transparent minerals, translucent minerals partially let light pass through, and opaque minerals do not let any light through. A mineral type can exhibit more than one level of transparency, and, in fact, most transparent minerals also occur in translucent forms. Flaws, inclusions, and impurities degrade the transparency of a mineral. Many minerals exhibit some forms that are completely transparent and other forms that are completely opaque. Such minerals are labeled in the transparency section of this guide as transparent to opaque. A number of minerals may seem opaque, but when held to a light source seem to be letting a small amount of light pass through at its corners. A specimen with such characteristics is said to be transparent in thin splinters or transparent in thin sections. All minerals with a metallic luster are opaque. Most minerals with a submetallic luster are translucent in thin splinters. How to use transparency as an identification mark Transparency isn't normally used as an identification mark, but is just noted as a mineral property. It can, however, eliminate some mineral possibilities when trying to identify a mineral. Some minerals that are normally transparent may be clouded by inclusions and appear partially or fully opaque. In such cases, one must view the mineral through a light and see if any light passes through. How to test using transparency A mineral should always be viewed by placing it between the viewer and the light source if one wants to check its transparency. A distinction can be noticed between translucent, translucent in thin splinters, and opaque minerals.
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