Fundamentals of geology I. (lithosphere) 1 1. The formation of the Earth 1
Fig. 1.11. Diorite – a neutral plutonic rock – and its thin section
Download 9 Mb.
|
- Navigate this page:
- Fig. 1.12. Granite – a felsic plutonic rock – and its thin section
Fig. 1.11. Diorite – a neutral plutonic rock – and its thin section 
Fig. 1.12. Granite – a felsic plutonic rock – and its thin section Texture also is an important criterion for the naming of igneous rocks. The texture of igneous rocks includes the size, shape, orientation, and distribution of mineral grains and the intergrain relationships. 1. Phaneritic textures are typical of intrusive igneous rocks, these rocks crystallized slowly below the Earth's surface. As a magma cools slowly the minerals have time to grow and form large crystals. The minerals in a phaneritic igneous rock are sufficiently large to see each individual crystal with the naked eye. Examples of phaneritic igneous rocks are gabbro, diorite and granite (Pict. 1.1.). 2. Porphyritic textures develop when conditions during cooling of a magma change relatively quickly. The earlier formed minerals will have formed slowly and remain as large crystals, whereas, sudden cooling causes the rapid crystallization of the remainder of the melt into a fine grained (aphanitic) matrix. The result is an aphanitic rock with some larger crystals (phenocrysts) imbedded within its matrix. Porphyritic texture also occurs when magma crystallizes below a volcano but is erupted before completing crystallization thus forcing the remaining lava to crystallize more rapidly with much smaller crystals. Examples of porphyritic igneous rock include basalt, andesite and rhyolite (Pict .1.2.). 3. Aphanitic rocks in contrast to phaneritic rocks, typically form from lava which crystallize rapidly on or near the Earth' surface. Because extrusive rocks make contact with the atmosphere they cool quickly, so the minerals do not have time to form large crystals. The individual crystals in an aphanitic igneous rock are not distinguisable to the naked eye (Pict .1.3.).  
Directory: tartalom -> tamop412A tamop412A -> Agricultural Economics II. Popp, József Agricultural Economics II tamop412A -> Ethology practical Vilmos Altbäcker Márta Gácsi András Kosztolányi Ákos Pogány Gabriella Lakatos tamop412A -> Operating Systems Lecture Notes Attila Dr. Adamkó Operating Systems Lecture Notes tamop412A -> Agroinformatics Herdon, Miklós Agroinformatics tamop412A -> Paternoster of Programmers Reloaded tamop412A -> Lőrincz, András Mészáros, Tamás Pataki, Béla Embedded Intelligent Systems tamop412A -> This course is realized as a part of the TÁmop 1 A/1-11/1-2011-0038 project tamop412A -> Computational biochemistry ferenc Bogár György Ferency Download 9 Mb. Share with your friends:
|