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The chemical formula of mineral Chalcocite is indicated by Cu2S or Copper Sulfide. Chalcocite is actually a Sulfide mineral. The name of the mineral species Chalcocite was actually derived from the Greek word chalkos, which means copper. Chalcocite mineral is also sometimes called as vitreous copper, redruthite and also as copper glance. At temperature below 105 degrees Celsius, Chalcocite minerals are known to crystallize in the orthorhombic system, which can be seen clearly with the aid of geological microscopes. This crystal system comprises crystals having three mutually perpendicular axes, of which all are of different lengths. At temperature above 105 degrees Celsius, Chalcocite crystallizes in the hexagonal system. The hexagonal system of crystallization comprises crystals having four axes. Three of which are positioned in a single plane with equal length and are symmetrically spaced. The fourth axis is found to be perpendicular to the other three axes.


            Chalcocite mineral is also considered as minor ore of copper and it is often found exhibiting interesting images when viewed under an ore polarizing microscope for geologists. It is actually an important copper mineral ore. They are commonly used as mineral specimen and often found exhibiting splendid microscope appearance under polarizing light microscopes used in optical mineralogy. Chalcocite is actually one of the most important and profitable copper ore and it has been mined for centuries now. Chalcocite has a very high copper content, which is almost 67 percent atomic ratio and 80 percent by weight, and it can be easily separated from sulfur. But since this mineral Chalcocite is a considerably rare mineral, it is not considered as the primary copper ore. Chalcocite minerals are still being mined from the richest deposit of the said mineral and may be would still be mined in the future despite the fact that it has been probably mined out centuries ago.


            Fine mineral crystals of Chalcocite are considered as much sought after specimen because they are quite very uncommon in occurrence. The most wonderful and famous Chalcocite crystals in cluster forms are commonly produced by the now depleted mines located at Cornwall, England and in Bristol, Connecticut in the United States. There are also some other types of localities that formed promising well-formed Chalcocite crystals but those that are produced by the old mines mentioned above are the ones that are found in the mineral market. Those classic Chalcocite mineral crystals that commonly command a classic price are usually heavily striated and in form of pseudohexagonal tabular crystals.


            Chalcocite is usually found forming pseudomorphs to many different minerals, since they are secondary minerals that form from the alteration of other interesting minerals. In optical mineralogy, a pseudomorph mineral can replace the chemistry of another mineral atom by atom without changing the original crystal shape of the replaced mineral. The chemistry changed but the crystal structure remains the same and left intact. Pseudo means false and morph means shape or form. Thus, a pseudomorph is false shape of a certain pseudomorphed mineral. Chalcocite minerals are commonly known forming pseudomorphs of several other minerals such as pyrite, chalcopyrite, bornite, sphalerite, galena, millerite, covellite and enargite.


                        Chalcocite is most commonly found exhibiting dark gray to black color in reflected light of polarized microscopes for mineralogists. Chalcocite is usually found showing metallic luster when viewed in reflected light of petrographic polarizing microscope used in optical mineralogy. Chalcocite is usually found having imperfect prismatic cleavages in two directions when mineral specimen is evaluated between crossed nicols of polarizing light microscope for mineralogists. Chalcocite is also usually found showing conchoidal fracture when the mineral is evaluated under several adjustments on the aperture diaphragm of the polarizing microscope used in optical mineralogy. The specific gravity measure of the mineral Chalcocite usually gives an approximate value ranging from 5.5 grams per cubic centimeters to 5.8 grams per cubic centimeters, which is commonly considered above average for metallic minerals. The hardness measure of the mineral Chalcocite when it is evaluated using the Mohs scale method is commonly found ranging from 2.5 to 3. Chalcocite is most commonly found leaving a shiny black to lead gray streak when mineral specimens are rubbed on a white porcelain streak plate.


            Chalcocite mineral crystals are commonly found opaque in appearance. The crystal habit of Chalcocite as described in optical mineralogy field usually includes pseudohexagonal tabular to prismatic crystals, which are often found with a shallow pyramidal truncation with a flat point when viewed under polarized microscopes for mineralogists. This habit is commonly splendidly displayed under geological polarizing microscopes used in optical mineralogy. Some Chalcocite minerals are also found in massive and compact forms, which are usually exhibiting nice and interesting microscope images under polarized light microscope. These Chalcocite mineral crystals are commonly twinned and this twinned crystals sometimes results in a six pointed star shaped cyclic twin called trilling or in elbow shaped twins, which are seen more clearly visible when viewed with the aid of a petrographic polarizing light microscope used in optical mineralogy. Some Chalcocite crystals are usually found deeply grooved with lateral striations and they commonly tarnish resulting to a dull luster in reflected light of polarizing light microscopes. Chalcocite mineral crystals are also sectile. There is no specific data on the toxicity and health dangers for this mineral Chalcocite. However, the specimens of this mineral should be treated with great care and use of sensible precaution is advised upon handling them. This mineral actually dissolves easily in nitric acid and it decomposes in a flame usually giving off sulfur dioxide fumes. Chalcocite minerals are not radioactive. These minerals are also non-magnetic. They also show weak anisotrophism when viewed under petrographic polarizing light microscope.


Chalcocite commonly occurs as secondary mineral in many ore bodies that are found in the supergene enrichment zone. Thus, Chalcocite is also known as a secondary enrichment mineral. This actually remains true even though Chalcocite is also considered as a primary mineral as well. This mineral Chalcocite also forms from the alteration of primary copper minerals, which are usually attacked by oxygen above the water table. Mineral Chalcocite is a sulfide mineral, which is actually a copper reduced mineral. This is actually a result of the descending of copper fluids to the water table where this reaction process occurs with primary ore minerals. The ore bodies are usually found having chalcocite blanket or the layers of mineral Chalcocite, which commonly corresponds to the past or present level of the water table. It can be found that the Chalcocite blanket has richer copper content than the upper oxidized portion of the ore body and is also considered richer than the unaltered primary ores that are found just below. These Chalcocite layers or blanket actually represents a real gold or copper mine for most copper prospectors.


            Mineral Chalcocite is commonly associated with several other interesting minerals such as quartz, malachite, enargite, tetrahedrite, copper, bornite, azurite, cuprite, tennantite, covelite, chalcopyrite, pyrite and several other sulfide minerals. The best field indicators of mineral Chalcocite usually include color, streak, crystal habit, striations and its wonderful association with many other minerals producing a splendid and majestic piece of specimen that can be attractive to view under polarized microscopes. Mineral Chalcocite is also considered as a primary vein mineral in hydrothermal veins. Sometimes, this mineral can be also found in some sedimentary rocks. It can be also found in some ore veins and also in some sulfide deposits. These Chalcocite minerals notably occur at some types of localities including some areas in the United States such as Bristol, Connecticut, Butte, Montana, Morenci and Bisbee, Arizona, Bingham Canyon, Utah and Ducktown, Tennessee as well as some other localities like Tsumeb in Namibia, Rio Tinto in Spain, Tuscany in Italy and also in Cornwall, England.

Monday, December 29th, 2008 at 6:30 am
The Sulfides Mineral Class
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