The Geological Uses of A Petrographic Microscope
A petrographic microscope can also be used for geological purposes. It has the ability to define what kind of geological time scale the specimen is from. It can narrow down the various eons, periods, eras and epoch and specify it to the single time frame.
The scientist using the petrographic microscope must be equipped with the needed knowledge on earth anatomy, specifically plate tectonics and earthquake levels in order to maximize the information that the petrographic microscope can reveal from the experiments.
A petrographic microscope can obtain the specific physical properties of the cations. It can also find the common forming minerals and elaborate what kind of material it is – alkali feldspar, amphibole, biotite, magnetite, olivine, dolomite, gypsum, halite, calcite, hermatite, muscovite, pyroxene, plagioclase or quartz.
It can also determine what kind of ideal mineral can be found in the specimen – orthoclase, anorthite, olivine, magnetite, calcite, halite, gypsum, dolomite, hematite, quartz or albite.
Most importantly, the scientist must have the common knowledge of these rock forming minerals as well as the igneous, sedimentary and metamorphic rocks that will be encountered in the entire procedure. It also helps to have a knowledge of the distribution of the mineral as well as the geological origins.
Sedimentary Petrology
Essentially, the petrographic microscope can identify the sedimentary varieties of the rocks on a megascopical level. With the aid of various keys such as sandstones, feldspathic and lithic arenites, conglomerates and breccias, siltstone, claystone and shale, mudstone, packstone, boundstone, crystalline, grainstone, waskestone, limestones and dolostones and mudrocks.
It can also identify the minerals that do not contain the following keys mentioned earlier. These fossils are then grouped according to their taxonomic levels by using the various minerals: mollusks, corals, echinoids, trilobites and brachiopods.
The microscope can also help the scientist explain the relation of the rock to mineralogy and geology. It also underlies the divisions and the designs of the specimen on a grain size scale and figures out the relationship between the millimeter size as well as the phi size notations. It also explains the composition, sorting, sphericity, intraformational, marl, fossility, diamictic, roundness and modal size of the specimen.
Finally, the petrographic microscope explains the diagenetic process which includes the compaction, dolomitization, silicification and cementation of the material.
Procedures:
1. In order to fully identify the rock-forming mineral as well as the rock texture with the aid of the petrographic microscope, the scientist must identify the section where the sedimentary rock variety has the following – quartz, arenites, conglomerates, mudrocks, mudstone, limestones, claystone and shale, siltstones and dolostones.
2. Identify the section where the main minerals are located even without using the keys that have been mentioned previously. These minerals differ because of the subvarieties due to the extinction pattern. These include the chalcedony, plagioclase, mica, calcite, gypsum, hematite, pyrite, ilite/sericite-smectite, kaolinbite, chlorite, bituminous matter, limonite, anhydrite, dolomite, glauconite and alkali feldspar.
3. Identify the fossils that are found in the thin sections of the taxonomic groups using the following – algae, mollusks, coral, echinoids, trilobites, brachiopods and foraminifera.
4. The petrographic microscope explains the composition and texture of the specimen – from the modal size, sorting, unimodal or bimodal quality to the skewness, grain size, roundness, phi size notation and fossility. Other aspects it covers includes the diamictite, grain survivability, intraformational and multicyclic grains.
5. The contraption also explains the compositional and texturity maturity concepts of the specimen being observed. It recognizes the thin sections – be it compaction, clay mineral transformation, dissolution and replacement, pressure solution, dust ring formation, styolitization, silicification, vein filling, dolomitization, microbial micrtization, fracturing, pyritization, pologonization, epitaxial overgrowth, secondary porosity formation, sericitization, clay matrix formation and cementation.
6. It then interprets the rock petrography of the specimen and predicts the provenance. It also determines the source area composition, climate, plate tectonic setting, distance and relief. All these information retrieve the carbonate rock petrography that is used in interpreting the deposition of the environment.
The important element in the whole procedure is the plane polarized light because it makes the mineral stand out from its surroundings. It also determines the difference between the surroundings and the refractive index of the specimen. These minerals stand out simply because it receives the plane polarized light.
The shape of the mineral is also important because this pretty much gives the scientist the characteristics he needs in order to discover what kind of mineral the element is. The chemical and physical weathering of these various modes affect the morphology of the mineral being observed. Regardless, they continue to appear in their original geological form which the petrographic microscope can still decipher.
