1 Sep In order to create a sustainable classification of igneous rocks which all geologists might use, an international body was set up by the IUGS: the. 18 Mar A classification of the phaneritic igneous rocks. b. Gabbroic rocks. c. Ultramafic rocks. After IUGS. 1/17/ Petrology-Spring , Goeke. basic system which classifies rocks on the basis of where they form. work by the IUGS Subcommission on the Classification of Igneous Rocks or Streckeissen .

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After silica, alumina is the second most abundant oxide constituent in igneous rocks. Note that this diagram is not used for all plutonic rocks.

Most are what we term genetic. Three possible conditions exist.

For our purposes, we will introduce and discuss a much simpler classification that will allow us to easily identify the more common cassification rocks. In other projects Wikimedia Commons.

The QAPF diagram has four minerals or mineral groups chosen as important cornerstones of the classification. Not really, these are the minerals that should crystallize ougs a dacite magma, but don’t because the crystallization history is interrupted by rapid cooling on the surface.

All compositions between En and SiO 2 will end iugs classification of igneous rocks crystallization with quartz and enstatite. Examples of Questions on this material that could be on an Exam. Let’s imagine first a composition in the silica-undersaturated field. Chemical composition cannot be igenous determined in the field, making classification based on chemistry impractical. Minerals Present in the Rock the mode. Rock classifications also seek to reduce complexity. Chemical analyses can be obtained, and a chemical classification, iugs classification of igneous rocks as the LeBas et al.


Cooling to anywhere on the liquidus will result in the crystallization classificatioj Fo-rich olivine.

QAPF diagram

That means that by pigeonholing a rock in a certain group we say something about its genesis or igneouw. Remember that porphyritic rocks have spent time in both worlds.

Iugs classification of igneous rocks is partly due to historical reasons, partly due to the nature of magmas, and partly due to the various criteria that could potentially be used to classify rocks. SiO 2 diagram shown below. The composition usually reflects the composition of the magma, and thus provides information on the source of the rock.

iugs classification of igneous rocks Let’s first examine the classification of plutonic rocks. We can easily the inadequacy of a mineralogical classification based on minerals present if you look at the classification schemes for volcanic rocks given in introductory geology textbooks. Note how compositions between Fo and Clazsification will end their crystallization with only Fo olivine and enstatite.

In the field, a simple field based iugs classification of igneous rocks must be used. Silica Undersaturated Rocks – In these rocks we should find minerals that, in general, do not occur with quartz. Generally, rocks that contain lots of gineous and quartz are light colored, and rocks that contain lots of pyroxenes, olivines, and amphiboles ferromagnesium minerals are dark colored.


The IUGS systematics of igneous rocks

The chemical composition of the magma determines the minerals that will crystallize and their proportions. TAS is also used if volcanic rock contains volcanic glass such as obsidian. Because they are solutions, their chemical composition can vary continuously within a range of compositions. General Classification of Igneous Rocks.

The IUGS systematics of igneous rocks | Journal of the Geological Society

The minerals present in a rock and their relative ifneous in the rock depend largely on the chemical composition of the magma. September Learn how and when to remove this template message. The silica saturation concept can thus be used to divide rocks in silica undersaturated, roccks saturated, and silica oversaturated rocks. These rocks can be identified as possibly any rock that does not contain one of the iugs classification of igneous rocks in the above list.

Feldspars are, in general, the most abundant minerals that occur in igneous rocks.