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Archive for April, 2008

Dolomite

Monday, April 28th, 2008

The chemical formula of Dolomite is indicated by CaMg(CO3)2 or Calcium Magnesium Carbonate. Dolomite is a Carbonate mineral. It is known to crystallize in the hexagonal system. In optical mineralogy, 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. […]

Parallel and Convergent Polarized Light

Monday, April 28th, 2008

In optical mineralogy, the kind of light used in detecting the pleochroism property of the mineral, in studying the interference colors, in locating the direction of vibration, in determining the strength of the double refraction, in measuring extinction angles, in distinguishing whether the mineral section is isotropic or anisotropic, in finding the direction of vibration […]

Optical Distinction Between Orthorhombic, Monoclinic, and Triclinic Minerals

Monday, April 28th, 2008

In optical mineralogy, it is greatly understood that the interference figures are always symmetrical in shape and distribution of color to the planes and axes of symmetry of the crystal system. They are most symmetrical in orthorhombic, less so in monoclinic, and still less in triclinic crystal system.               The figures found exhibited by […]

Interference Figures of Uniaxial Minerals

Monday, April 28th, 2008

Interference figures of uniaxial minerals can be best viewed with the use of petrographic polarizing microscopes. In optical mineralogy, a dark cross that can be found with or without rings can be found as shown by sections positioned perpendicular to the optic or vertical axis c. When the section is closely evaluated, it can be […]

The Optical Character of Uniaxial Interference Figures

Monday, April 28th, 2008

The section should be test by means of a one-fourth undulation mica plate after having obtained a uniaxial interference figure. The mica plate is usually introduced between the objective and the analyzer of the polarizing microscope in such a way that its vibration direction c, which is marked on the plate, makes an angle of […]

Interference Figures of Biaxial Minerals

Monday, April 28th, 2008

Interference Figures of biaxial minerals is one of the concerns of mineralogists in optical mineralogy. It can be best determined with the test made with the use of petrographic polarizing light microscope. The curves being nearly circular and a straight black bar bisecting these curves can be found as interference figure exhibited by sections perpendicular […]

Optical Character of Biaxial Interference Figures

Monday, April 28th, 2008

The methods used for testing uniaxial figures are employed when the axial angle is very small, so that the interference figure approaches that of a uniaxial crystal. However, in optical mineralogy, there are several methods used if the axial angle is large.               The stage of the petrographic polarizing microscope is rotated until the […]

Optical Characters of Minerals Observed by Convergent Polarized Light

Monday, April 28th, 2008

In optical mineralogy, Convergent Light is usually obtained by passing the rays of polarized light through a strong condensing lens of petrographic polarizing microscope. This lens generally fits like a cap over the top of the polarizer. The condensing lens of the polarizing microscope can be brought very close to the lower surface of the […]

Structures of Minerals

Monday, April 28th, 2008

One of the features of minerals that need extra care upon identification of minerals in optical mineralogy is their structure. Twinning is one of the structures that need to be carefully evaluated and this can be done more accurately when the mineral is viewed with the aid of the petrographic polarizing light microscope. Minerals usually […]

The Characters of Opaque Minerals

Monday, April 14th, 2008

        These characters of opaque minerals can be only discussed in optical mineralogy if rightly evaluated in reflected light of polarizing microscope. Most minerals that remain perfectly opaque from hand sample to thin section are most likely to exhibit a metallic luster under petrographic polarizing microscope. These samples are also very minute in size […]

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