| Pict. 1.1. Granite - phaneritic texture Pict.1.2. Andesite - porphyritic texture Pict.1.3. Rhyolite - aphanitic texture
For igneous rocks where all minerals are visible at least via microscope, the mineralogy is used to classify the rock. This usually occurs on ternary diagrams, where the relative proportions of four minerals. These are quartz (Q), alkali feldspars (A), plagioclase feldspars (P), and feldspathoids (F). F and Q for chemical reasons cannot exist together in one plutonic rock. Other minerals may and almost certainly occur in these rocks as well but they have no significance in this classification scheme. The whole diagram is actually composed of two ternary plots (QAP and FAP). To use the classification, the concentration (the mode) of these minerals must be known and recalculated to make their sum 100%. This system was worked out by Streckeisen (Báldi 1991, Szakmány – Józsa 2008) (Fig. 1.13.).
Fig. 1.13. Place of igneous rocks in the Streckeisen diagram
1.4.2. 1.4.2. Sedimentary rocks
Sedimentary rock is a type of rock that is formed by sedimentation of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles (detritus) to settle and accumulate or minerals to precipitate from a solution. Particles that form a sedimentary rock by accumulating are called sediment. Before being deposited, sediment was formed by weathering and erosion in a source area, and then transported to the place of deposition by water(Fig.1.14.), wind, mass movement or glaciers which are called agents of denudation.
Share with your friends: |
