Leave a message

Click Here For Best Selection Of High Quality Polarizing Microscope

Click Here For Best Selection Of High Quality Polarizing Microscope

The geometrical shapes of uniaxial minerals usually include tetragonal or hexagonal. These uniaxial minerals possess a high degree of symmetry about the c crystallographic axis and this is the most common characteristic of these minerals. It can be also found that with the plane {001} or {0001}, there is uniform chemical bonding found in all directions. The plane is usually found at right angles to the c-axis. There is also a different strength bonding between these planes. This property is clearly and nicely illustrated by the structure of the mineral calcite when evaluated with the aid of the petrographic polarizing light microscope. The chemical construction of mineral calcite is made up of the alternating layers of calcium ions and triangular carbonate anion groups parallel to the plane {0001}. Considering all the directions within the planes of ions, the electronic environment and the chemical bonding is uniform all over. The chemical bonding is also very different from the bonding between the planes.

            There is also an equally free vibration to any directions within the plane {001} or {0001} if the light would travel along the c-axis. The light is not split into two rays because there are no preferred directions of vibration in this plane. Just like how it behave in an isotropic mineral, it would just simply easily pass through the mineral. On the other hand, it finds a different electronic environment for different vibration directions if light passes at some angle to the c-axis. And then, the light is split into two rays with different velocities. It can be found that when the ordinary ray vibrates, its vibration vector is parallel to the {001} or {0001} plane. Then, the extraordinary ray on the other hand would vibrate across these planes. Regardless of path, the ordinary ray has the same velocity because it always vibrates in the same electronic environment. However, the velocity of the extraordinary ray varies depending on its direction. The extraordinary ray vibrates almost parallel to plane {001} or {0001} if the light travels almost parallel to the c-axis. The prime index of extraordinary ray is almost the same as the index of the ordinary ray because the extraordinary ray encounters almost the same electronic environment as the ordinary ray. The index of the extraordinary ray will be very different from that of the ordinary ray if the light would travel at right angles to the c-axis resulting to the vibration of the extraordinary ray directly across the planes {001} and {0001}. If the extraordinary ray vibrates at an angle to plane {001} or {0001} following an intermediate direction, the prime index of the extraordinary ray will also be intermediate. The chemical bonding and crystal structure of the mineral speaks whether the extraordinary ray has lower or higher index when compared to the index of the ordinary ray.



Author:
Time:
Monday, March 24th, 2008 at 4:23 am
Category:
Optical Mineralogy
RSS:
You can follow any responses to this entry through the RSS 2.0 feed.
Navigation:
Click Here For Best Selection Of High Quality Polarizing Microscope