GL23C IGNEOUS & METAMORPHIC PETROLOGY LAB 2 |
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You have been provided with a number of plutonic rock hand specimens by your instructor. You must give a detailed description of each hand specimen, by describing its colour (using C.I. terminology), its texture (phaneritic/ porphyritic-phaneritic/ pegmatitic etc.), its mineralogy (essential minerals and their modal percentage), any peculiar features (layering, xenoliths, etc). Finally you must classify each rock specimen using IUGS Field Classification nomenclature. As a guide to your hand specimen description it is advisable to follow a particular format. For example, you should have an opening paragraph which describes the colour (leuco-,meso-,melano-cratic), texture, and the minerals present (giving approximate modal mineralogy) in the rock. If there are any unique or peculiar features viz. layering, xenolths, xenocrysts etc., these should also be included/described in the opening paragraph. The following paragraphs should contain a more detailed description of the individual minerals in the rock, such as the shape, size, colour, etc., of each mineral. Eg.`Biotite is scattered throughout the rock and makes up approximately 20% of rock volume. The mineral is black in colour, shows a prominent cleavage, has a subhedral shape and varies in size from 1 mm to 2 mm. The edges of some of the larger crystals contain a light green mineral, possibly chlorite, which indicates that the rock has undergone secondary alteration.' The final paragraph should contain your IUGS calculations, i.e. the amount of Q/F,A,P in the case of rocks with <90% mafic minerals, or the amount of Ol,Pyx,Hbl, etc.,in the case of the ultramafic rocks, and the field name based on your calculations. List of Plutonic Rocks to be Examamined in Lab 2
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