The Proper Way To Petrographic Sample Preparation
A petrography microscope is a special type of microscope used to examine the characteristics of minerals. What it does is to reflect the mineral’s properties so that they can be easily identified under the lenses of the microscope. Petrography microscopes are usually compound microscopes working on a plane polarized light. As such, peculiarities in the sample can be somewhat expected.
To use a petrographic microscope, the plane polarized light transmitter should always be inserted and in place. And due to the presence of the polarizer, it follows that the illumination system of this type of microscope can either be orthoscopic or conoscopic. Orthoscopic corresponds to the light in a parallel position. This illumination technique doesn’t use a condenser. On the other hand, the conoscopic lighting system is convergent and commonly uses a condenser.
Using petrographic microscope require special sample preparation. It works very much unlike a traditional light microscope where in samples are merely placed over the slide and placed under the microscope’s probes. The samples to be viewed under a petrography microscope have to be specifically set up for proper optical identification.
First and foremost, the size of the minerals to be observed should be 0.010 millimeters or so. Users of the microscopes, who usually are geologists, have to take a minuscule part of their samples with the right thickness in order to properly analyze them. The types of samples commonly viewed under this type of microscope are rocks, sediments, and precious stones.
Here are the step-by-step procedure on how to make a prepare a petrographic sample for view under the microscope:
1. Cut a thin section of the sample to be observed.
A small part of the specimen should be obtained from the original rock sample. As stated earlier, the ideal size is no more than 0.010 millimeters thick. The specimen should also be polished so that the minerals it contains will be detected easily under the microscope’s obtrusive lenses.
2. Mount the sample on the glass slide.
To do this, a clear epoxy is needed. The thin sample should be adhered to the slide. This ensures that the sample won’t move out view. Doing so also prevents the air from blowing them off away while you were busy inspecting them with a microscope.
3. Ground the sample, if possible.
The mineral sample is best viewed if it is finely grounded. For softer samples, merely crushing the rock with one’s bare hands should do the trick. But for denser rock samples, a mechanical sectioner may be required. Grounding the sample is usually done for cursory study. The ideal thickness of the ground sample is more or less thirty microns. Grounding the sample allows the light to go through it. And due to the natural-occurring crystalline feature of minerals, light is effectively refracted from the source, to the sample, and towards the eyepiece tubes. And as the light travels, it is made to pass through a prism. The prism is the main element that creates an absolute image of the sample being observed.
After following the steps above, the samples should be ready. Generally speaking, a petrograpic microscope is composed of three major parts. These are the head, stage and the substage, and lastly, the base. The head is where the eyepiece is attached. Petrographic microscopes can either be monocular or binocular microscopes. It is also a compound microscope having as many as five objectives. The most important element of the head is the prism.
The stage is where the sample is placed. Most of the stages of petrographic microscopes can be moved and rotated at 360 degrees. It is the mechanical stage that actually allows polarized light to pass through at different angles. On the other hand, the sub-stage is the part that houses the condenser, which also plays role an important role in the illumination process.
The base of the petrographic microscope doesn’t only serve as its stand. The base also holds the light source of the microscope, which is usually a 15-watt light bulb. This only shows that the light of the sample comes from the bottom then directed upwards. And as light travels, it made to pass through a filter. All the adjustment knobs are also attached to the base.
The proper use of petrographic microscope depends entirely on the correct preparation of mineral samples, as well as the adequate knowledge of the user regarding how the microscope works. For additional information about petrographic microscopes and its uses, log on to petrographic-microscope.com. The site is rich with important details about this special microscope.
For more information, please visit http://www.petrographic-microscope.com/
