Image by Modris Baum ( ), „Argentiferous Galena-458851“, marked as public domain, more details on Wikimedia Commons: John ( (high-grade_iron_ore)_(Soudan_Iron-Formation,_Neoarchean,_~2.69_Ga _Soudan_Mine,_Soudan,_Minnesota,_USA)_2_(18844370038).jpg), „Specularite (high-grade iron ore) (Soudan Iron-Formation, Neoarchean, ~2.69 Ga Soudan Mine, Soudan, Minnesota, USA) 2 (18844370038)“, Modreski, USGS Communications and Outreach, and the Brigham Young University (BYU) Geology Department This image is in the public domain pursuant to an agreement dated Augbetween Peter J. Mineral collection of Brigham Young University Department of Geology, Provo, Utah. Image by DerHexer, Wikimedia Commons, CC-by-sa 4.0 ( (Ceylon)_Sri_Lanka_(DerHexer)_.jpg), Non-metallic luster - coarser-grained crystals of quartz (gray). Metallic luster - fine-grained crystals of pyrite (brassy yellow). Metallic luster - crystalline aggregate of graphite. Metallic luster - single crystal of graphite. Here are some examples of luster in rocks (multi-crystalline aggregates) where crystals approach microscopic in size, making luster more difficult to evaluate. Make sure you observe other properties (e.g., hardness, streak, cleavage, etc.) Don't spend too much time on evaluating luster of rock samples. That's why you'll need to examine a sample to determine multiple properties that help you to narrow down a list of possible names for identification. The determination of luster becomes more difficult and uncertain as crystal size becomes smaller, eventually microscopic. The above examples show single crystals of significant size for handling and observation. The crystal is translucent.Ī mineral, by definition, is a solid chemical compound with ions and molecules arranged in long-distance, repetitive, geometric order. Note that you can see that light penetrates inside of the crystal. Non-metallic luster - single crystal of calcite (dogtooth spar). Note that you can see the inside of the crystal. Non-metallic luster - single crystal of quartz (smoky). Non-metallic luster - purple cubic crystals of fluorite. Metallic luster - brownish cubic crystals of galena. For more details about the different terms given for luster, consult this link - luster in mineral identification. Terms used for non-metallic luster include glassy (or "vitreous"), pearly (like mother-of-pearl), etc.
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