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Monthly archives: August, 2021

Dip and Strike

Basically the beds of the sedimentary rocks are found in horizontal disposition. But due to the earth movement and ground disturbance, these beds of the sedimentary rocks get inclined and loose their horizontal position. The tilted strata and the inclination of rock beds is known as ”dip”. The object of measuring dip and strike of …

Observations in convergent light

If we examine the sections of an-isotropic minerals under a convergent polarized light, the ”interference figures” can be seen. In order to observe these figures, we need to make some pre-adjustments in the polarizing microscope. Polars are crossed. Condenser lens is used below the stage to produce a converging beam. A high power objective is …

Accessory plates used with polarizing microscope

There are some standard accessory plates used with a polarizing microscope to examine the optical properties of minerals. Some of the accessory plates are (i) quartz wedge, (ii) gypsum plates, and (iii) mica plates. (1). Quartz Plates: The quartz wedge is a very thin wedge-shaped plate of quartz in which the fast vibration direction is …

Extinction Direction of the minerals during optical analysis

When vibration directions of an anisotropic mineral coincide with those of the polarizer and analyzer, the mineral appears dark. This position of an anisotropic mineral is called ”position of extinction”. During a complete rotation of the microscope stage, the position of extinction occurs four times at 90┬░┬áintervals. In extinction position, the light from the polarizer …

Examination of Minerals in Cross Polars

Examination of Minerals in Crossed Polars: When the analyzer is placed in the position with its plane of polarization at right angles to that of the polarizer, the polars are said to be ”crossed”. If a section of a doubly refracting mineral is placed between crossed polars, the light is doubly refracted and polarized three …

Polarizing Microscope

A polarizing Microscope is also known as the Polarized Light Microscope. The optical properties of minerals can be determined with the help of a Polarizing Microscope. In order to study minerals under a polarizing microscope, their thin sections of about 0.035 mm thickness are placed on the rotating stage of the microscope and examined. Main …

Optical Indicatrix of Minerals

In anisotropic minerals, the refractive index varies with the crystal direction. This relationship can be illustrated with the help of a geometrical figure called the ”optical indicatrix”. The optical indicatrix of an anisotropic crystal is an ellipsoid whose semiaxes are proportional to the refractive indices in the respective directions. In the crystals of cubic system …