The Evanescence of the Art of Petrography
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we see the glory of rocks through the narrow slit of a microscope. Micro textural evidences are commonly used to infer metamorphic reactions, which, in turn, are utilized to deduce Pressuretemperature-time paths and provide information on the metamorphic evolutionary history of regional terrains. The ‘art of petrography’ is an important aspect of petrological investigations. The spectacular textures in the rocks reflect the extraordinary potential information they conceal within their tiny domain. There is every reason to believe “that when the first relic textures were forming, the first rocks were too”. Petrography is that branch of ‘Petrology’ which focuses on the detailed descriptions of rocks. The mineral content and the textural relationships within the rock are described in detail. Petrographic descriptions start with the field notes at the outcrop and include mesascopic description of hand specimens. However, the most important tool for the petrographer is the petrographic microscope. The detailed analysis of minerals by optical mineralogy in thin section and the micro-texture and structure are vital to understand the origin of the rock. EPMA analysis of individual grains as well as whole rock chemical analysis by ICP-MS is used in a modern petrographic lab when optical means are insufficient. The optical properties of minerals JOUR.GEOL.SOC.INDIA, VOL.96, DEC. 2020
are particularly important in distinguishing the different mineral species, compositional and structural variation within these species, as well as orientation within a rock fabric. Compositional and structural variations as well as the overall textures developed within rocks provide the geologists the basis for the interpretation of the genesis of rocks. However, in recent years there has been a significant decline in the mastery on the art of petrography. The lack of proper training and rigorous on-the-spot microscopic teaching of the petrographic observations have led to a loss of a very potential framework of interpretation. As a result, unfortunately, most of the students are ignorant about the microscopic distinction even between quartz and cordierite and inadvertently opt for costly techniques to extract relevant textural information. The correct textural details integrated with mineral-chemical data could provide accurate summary on mineral evolution history. Marking characteristic points for the specific area for EPMA would necessitate identification of mineral assemblages and encapsulation of subsequent analytical work on modern, highly sophisticated and expensive equipments which should follow these essential components of fundamental Geology. The negligence of the microscopic observational view point is presently common among the budding Earth scientists and its poor grasp clearly reflects the cause for the deteriorating standards. To sum up, it is important to learn about the strong influence of textural observations in Petrology, and it is time that students are shown what can the ‘Art of Petrography’ teach them. An illustrated exam
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