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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 mineral identification process is a systematic approach. May it be in thin section or grain mount, the process of identification should be tempered with the familiarity with variety of common rocks and minerals as well as with common sense in evaluation. It is also important to note that over 3000 different kinds of minerals known, there can be some instances when an uncommon may be present in any given rock sample.

            Minerals have several descriptive features. Among the most common as classified under crystal shapes are acicular or shapes like elongate needlelike grains, anhedral or without regular crystal faces, bladed or elongate and slender, columnar or shaped like a column with moderately elongate grains having equidimensional cross section, equant or equidimensional grains, euhedral or has well-formed crystal faces, fibrous or with individual grains that are long and slender fibers, lathlike or flat elongate grains, prismatic or with dominant faces that are those of a prism, subhedral or has crystal faces but they are poorly formed or irregular, and tabular or shaped like a book. Under mode of aggregation are columnar or with parallel arrangement of columnar grains, foliated or with more or less parallel tabular or platy grains, granular or with equant grains where they are all about of the same size, matted or having elongate grains in a random pattern, and radiating or having elongate grains that radiate out from a center.

            The presence of the cleavage is another way of identifying minerals. If the sample is in grain mount, the indication of the presence of a cleavage is the planar sides to the individual grains that can be seen more visibly when evaluated with the aid of polarizing microscope for mineralogists. There can be approximate angular relation between the cleavages if the grains are carefully observed under the geological polarizing microscope. If the sample is in thin section, the indication of cleavage is very poor. Most especially for mineral samples having low relief, the cleavage may be very difficult to recognize. However, the presence of the parallel cracks may be enhanced by careful examination of the minerals under several adjustments on the aperture diaphragm of the polarizing light microscopes. It has been found that in thin section, the angle between the traces of different cleavages depends on how the mineral has been cut.

            Twinning is another diagnostic property of minerals. Many of the known minerals are twinned with the nature of their twinning often easily seen with the aid of petrographic polarizing light microscope. The two segments that usually go extinct at different points during the rotation of the petrographic polarizing microscope stage are called simple twins. The ones that are joined by a smooth twin plane that separates the segments that can be seen under polarizing microscope are called contact twins. Penetration twins, on the other hand, are generally joined on irregular contacts and this can be also found more clearly visible with the aid of geological polarizing light microscopes. The twinning type consisting numerous twin segments joined on parallel twin planes visible under polarizing microscope for mineralogists is called polysynthetic twinning. Another special type of twinning is cyclic twinning. This type occurs if successive twin planes are not parallel.

            Alteration can be also considered as another distinctive property of minerals. This is because most of the minerals are subject to alteration through several causes like weathering, and several other processes like hydrothermal process. The identity of the original mineral is almost often obscured by the alteration process. But then this result can be of much importance and also considered useful diagnostic property of certain minerals. It is also very important to note that the optical properties of the remnants of the original mineral are significantly changed if the alteration process is so severe.

            Another important characteristic of minerals are the identification of their associated minerals. This can be very useful in recognizing minerals with almost the same features. This is because some minerals are commonly associated or found in certain rocks or mineral deposits. Some other minerals are rarely occurring together. Some never occurs with some specific minerals. Recognizing the associated minerals can also a great help in making educated guess about the identity of the unknown mineral. Similarly, mineral association can also suggest the presence of the overlooked mineral type that is present in the sample.



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Monday, March 24th, 2008 at 4:24 am
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Optical Mineralogy
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Click Here For Best Selection Of High Quality Polarizing Microscope