Some specimens fluoresce with an orange hue in ultraviolet light these also display triboluminescence, emitting orange flashes when stroked with a knife.Code: 11:57 Downloading CSharpCompiler.x86_圆4 for. It has excellent dodecahedral cleavage, which means that with careful hammer work you can chip it into nice 12-sided pieces. Sphalerite has some interesting properties. Miners call sphalerite "jack," "blackjack," or "zinc blende." Its impurities of gallium, indium and cadmium make sphalerite a major ore of those metals. Sphalerite can be found in many ore veins of sulfide minerals, commonly associated with galena and pyrite. It commonly occurs as tetrahedral crystals or cubes as well as in granular or massive form. Dark specimens can appear somewhat metallic in luster, but otherwise its luster can be described as resinous or adamantine. Most often sphalerite is reddish-brown, but it can range from black to (in rare cases) clear. Sphalerite (SFAL-erite) is zinc sulfide (ZnS) and the foremost ore of zinc. Photo courtesy Karel Jakubec via Wikimedia Commons And blocky pyrite crystals are commonly found in slate and phyllite. Pyrite also readily forms crystals, either cubic or the 12-sided forms called pyritohedrons. They are nodules of pyrite crystals that grew between layers of shale or coal. Pyrite "dollars" with a radiating habit are often found for sale at rock shows. Still, it's pretty, it's an important geochemical indicator, and in some places pyrite really does include silver and gold as a contaminant. Only a fool would mistake it for gold, which is why pyrite is also known as fool's gold. Pyrite resembles gold slightly, but gold is much heavier and much softer, and it never shows the broken faces that you see in these grains. Pyrite has a Mohs hardness of 6, a brass-yellow color and a greenish black streak. Pyrite occurs in this specimen in relatively large grains associated with quartz and milky-blue feldspar. Geochemically speaking, pyrite is the most important sulfur-containing mineral. Pyrite, iron sulfide (FeS 2), is a common mineral in many rocks. I'm guessing that the green, mealy-looking mineral is sphalerite (ZnS), but don't quote me. In this bornite specimen are also bits of golden metallic chalcopyrite (CuFeS 2) and areas of dark-gray chalcocite (Cu 2S). ![]() Bornite has a Mohs hardness of 3 and a dark gray streak.Ĭopper sulfides are a closely related mineral group, and they often occur together. That gives bornite the nickname peacock ore. ![]() (more below)īornite stands out for the amazing metallic blue-green color it turns after exposure to the air. The sulfide mineral specimens you see in rock shops come from the deep levels of mines, and most display a metallic luster.īornite (Cu 5FeS 4)is one of the lesser copper ore minerals, but its color makes it highly collectible. Sulfides also occur in metamorphic rocks where sulfate minerals are broken down by heat and pressure, and in sedimentary rocks where they are formed by the action of sulfate-reducing bacteria. Sulfides occur as primary accessory minerals in many different igneous rocks and in deep hydrothermal deposits that are closely related to igneous intrusions. The sulfide minerals represent higher temperatures and a slightly deeper setting than the sulfate minerals, which reflect the oxygen-rich environment near the Earth's surface. Photo (c) 2009 Andrew Alden, licensed to ( fair use policy)
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