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Click Here For Best Selection Of High Quality Polarizing Microscope

Click Here For Best Selection Of High Quality Polarizing Microscope

The chemical formula of mineral Bournonite is indicated by CuPbSbS3 or Copper Lead Antimony Sulfide. Bournonite actually belongs to the Sulfides mineral class. Bournonite was first discovered in the year 1805 at the Wheal Boys in the parish of Endellion in Cornwall, England. But before this, Philip Rashleigh first mentioned Bournonite as an ore of antimony in the year 1797. Bournonite mineral species was named after Count J.L. de Bournon (1751-1825), a French mineralogist and a crystallographer. In the year 1813, Bournon himself gave the name endellione, since it is actually used in the form of endellionite, which is after the locality in Cornwall, England where Bournonite mineral was first found. The mineral Bournonite is also sometimes called a cogwheel ore. This is for the reason that the shape formed by the twinned crystals of Bournonite is in shape of cogwheel. Bournonite minerals are also mined as an ore of lead, antimony and copper.


            Specimens of Bournonite are usually found in shades of silver gray or black when viewed in reflected light of petrographic polarizing microscope used in the field of optical mineralogy. Bournonite is commonly found exhibiting a metallic luster when viewed in reflected light of polarized microscope for mineralogists. The cleavage found when Bournonite mineral specimen is examined between crossed nicols of polarizing microscopes used in optical mineralogy is commonly poor in one direction. It has a subconchoidal fracture found under several adjustments on the aperture diaphragm of the polarizing microscope for geologists. In the field of optical mineralogy, subconchoidal fractures are known to develop in brittle materials characterized by semi-curving surfaces. In the field of optical mineralogy, fracture describes how a mineral breaks when broken contrary to its natural cleavage planes. The hardness measure of Bournonite mineral specimen when they are evaluated using the Mohs scale method is usually found in values ranging from 2.5 to 3.  Bournonite are usually found leaving a black streak when they are rubbed on the white porcelain streak plate. The specific gravity measure of mineral Bournonite usually gives an approximate value of 5.8 grams per cubic centimeters, which is considered above average for metallic minerals.


            Bournonite minerals are known to crystallize in the orthorhombic system of crystal formation. In optical mineralogy, this crystal system comprises crystals having three mutually perpendicular axes, of which all are of different lengths. Bournonite mineral crystals are commonly found opaque in appearance. The crystal habit of Bournonite as described in optical mineralogy commonly includes tabular, which are shaped like a book, to prismatic crystals. They can be also found as massive crystals and also granular in form. They may be also found formed as sub-parallel aggregates. Bournonite minerals are often found brittle, a property that is often displayed by glasses and most non-metallic minerals. These Bournonite minerals are commonly associated with other interesting minerals such as siderite, galena, pyrite, fluorite, calcite and sphalerite. Although Bournonite minerals show a bright luster in reflected light of polarizing microscope for mineralogists, they actually develop a dull tarnish. The crystals of Bournonite minerals are usually striated on their sides that are commonly found producing the teeth of the cogwheel, which are really interesting to view under petrographic polarizing microscopes used in optical mineralogy. A cogwheel is generally a six-sided twinned crystal forming the Cogwheel shapes. Sometimes they are found in platy sheets forms. They can be found as pseudocubic crystals that are usually showing a cubic outline that is clearly visible under polarized microscopes. This can be found clearly visible when Bournonite specimen is viewed with the aid of a polarizing microscope used in optical mineralogy.


Bournonite specimens are actually found displaying properties of anisotropic minerals when evaluated between crossed nicols of petrographic polarizing light microscopes used in the field of optical mineralogy. But they are actually weakly anisotropic. They are usually found weakly pleochroic when evaluated under a polarized microscope for mineralogists. Bournonite crystals are commonly twinned as found under polarizing microscopes used in optical mineralogy. And if these crystals of Bournonite are repetitively twinned, it can actually form a twinning type called trilling. Trilling actually is the formation of the four twins or crystals that are connected in a plane, which is clearly visible with the aid of petrographic polarizing microscope used in the field of optical mineralogy. Bournonite mineral crystals are usually found exhibiting polysynthetic twinning, which is in part due to deformation. These usually form a wheel with a jagged edge that is commonly found resembling the teeth of a cogwheel. Not all specimens however show this type of twinning when they are evaluated with the aid of a geological microscope. Bournonite minerals are commonly found fusing easily to a silvery, metallic globule with first a white then a yellow ring around the globule. Bournonite mineral specimen can be found decomposed by nitric acid. This usually gives a weak blue-green solution that becomes cloudy with a white precipitate of lead and sulfur, and also a skeletal yellow residue of sulfur. This Bournonite mineral is actually non-magnetic. Bournonite mineral specimens are found not radioactive after several chemical evaluations.


            Bournonite minerals are usually found formed in medium-temperature ore veins, which are commonly full of open cavities. They can also form in moderate temperature hydrothermal veins. They may be also found developed in mesothermal veins. Bournonite is considered as one of the commonest of the sulfosalt group. The best field indicators of Bournonite commonly include color, density and crystal habit as well as the twinnings that are found. Bournonite minerals notably occur in types of localities that include England, Australia, Mexico, Peru and also California in the United States.

Friday, January 15th, 2010 at 4:48 am
The Sulfides Mineral Class
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Click Here For Best Selection Of High Quality Polarizing Microscope