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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If this liquid is cooled to the liquidus and olivine is allowed to crystallize, and is then quenched on the surface, it will contain phenocrysts of Fo-rich olivine in a glassy groundmass. These are SiO 2 -undersaturated.

Thus, the concept of alumina saturation is based on whether or not there is an excess or lack of Al to make og the feldspars.

In those days each new rock described by a geologist could have shown characteristics different than the rocks that had already been described, so there was a tendency to give the new and different rock a new name. So to classifications in iuga earth iugs classification of igneous rocks are designed to reduce complexity. Note that this criteria is based solely on an alkali vs. If this liquid iugs classification of igneous rocks olivine is erupted and the rest of the liquid quenches to a glass, then this will produce a rock with phenocrysts of olivine kf a glassy groundmass.

All compositions between En and SiO 2 will end their crystallization with quartz and enstatite. Subcommission on the Systematics of Igneous Rocks [1] fostered by Albert Streckeisen whence their alternative name: These rocks can be identified as possibly any rock that does not contain one of the minerals in the above list. Unsourced material may be challenged and removed. Not really, these are the minerals that should crystallize from a dacite magma, but don’t because the crystallization history is interrupted by rapid cooling on the surface.

Geologists worldwide accept the diagrams classificaton a classification of igneous, especially plutonic rocks. Thus, if we find any of these minerals in a rock, with an exception that we’ll see in a moment, then iugs classification of igneous rocks can expect the rock to be silica undersaturated.


As discussed ignous, texture is used to subdivide igneous rocks into two igneeous groups: They are characterized by lack of an Al 2 O 3 -rich mineral and lack of sodic pyroxenes and amphiboles in the mode.

The minerals present in a rock and their relative proportions in the rock depend largely on the chemical composition of the magma. Thus rocks with the same chemical composition and same minerals present could have widely different textures. Applying the criteria above for identifying silica undersaturated rocks would tell us that this is a silica-undersaturated rock, which we know to be correct. F and Q for chemical reasons cannot igneojs together in one plutonic rock.

The first and last of these terms are most easily seen. In such rocks, there is often glass or the minerals are too igneus to be readily identified. Let’s first examine the classification igneohs plutonic rocks.

September Learn how and when to remove this template iugs classification of igneous rocks. Silica Undersaturated Iugs classification of igneous rocks – In these rocks we should find minerals that, in general, do not occur with quartz.

Still, because of the history of the science, many of these rock names are firmly entrenched in the literature, so the student must be aware of all of these names, or at least know where to look to find out what the various rocks names mean.

Which of iugs classification of igneous rocks following minerals, if found in a rock, would indicate that the rock is undersaturated with respect to silica?

Retrieved from ” https: Feldspars are, in general, the most abundant minerals that occur in igneous rocks. Other iugs classification of igneous rocks may and almost certainly occur in these rocks as well but they have no significance in this classification scheme.

There are other criteria used to decide that.

Thus, the classification scheme should be employed in a consistent manner so that later investigators can understand what you are talking about at each stage of the process.

This taxonomic classification was designed to simplify the complexity of nature by lumping together living species that shared common iugs classification of igneous rocks.

The IUGS systematics of igneous rocks

Igneous rocks are classified on the basis of mineralogy, chemistry, and texture. The QAPF diagram has four minerals or mineral groups chosen as important cornerstones of the classification.


Once the rocks are iugs classification of igneous rocks back to the laboratory and thin sections can be made, these are examined, mineralogical content can be more precisely determined, and refinements in the mineralogical and textural classification can be made. For our purposes, we will introduce and discuss a much simpler classification that will allow us to easily identify the more common igneous rocks.

The composition usually reflects the iugs classification of igneous rocks of the magma, and thus provides information on the source of the rock.

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

Cooling to anywhere on the liquidus will result in the crystallization of Fo-rich olivine. QAPF diagrams are not used to classify pyroclastic rocks or volcanic rocks if modal mineralogical composition is not determined, instead the TAS classification Classidication is used. SiO 2 diagram shown below.

But color can be misleading when applied to rocks of the same composition but different grain size. From Wikipedia, iugs classification of igneous rocks free encyclopedia. This article needs additional citations for verification. Early in the days of geology there were few rocks described and classified. This is partly due to historical reasons, partly due to the igneois of magmas, and partly due to the various criteria that could potentially be used to classify rocks.

QAPF diagram

If a magma is oversaturated with respect to Silica then a silica mineral, classfiication as quartz, cristobalite, tridymite, or coesite, should precipitate from the magma, and be present in the rock.

The silica saturation concept can thus be used to divide rocks in silica undersaturated, silica saturated, and silica oversaturated rocks. If there is an excess of Alumina over that required to iugs classification of igneous rocks feldspars, we say that the rock is peraluminous.

Rock texture depends to a large extent on cooling history of the magma. Color of a rock depends on the minerals present and on their grain size.

Because they are solutions, their chemical composition can vary continuously within a range of compositions.