Intermediate magmas are somewhat more viscous than the mafic magmas. We investigated this with an integrated petrological, mineralogical, geochronological, and geochemical study of the Chigu Tso tholeiitic intrusive suite (including dolerite, diorite, and tonalitic dykes and sills) in central Comei LIP, SE Tibet. The diagram in Figure 3.4.1 can be used to help classify igneous rocks by their mineral composition. Intermediate igneous rocks are those in which quartz accounts for 5% to 20% of the rock. Diorite (intrusive) and Andesite (extrusive) are the two most common types of intermediate rock. With your groups organize the igneous rock kit into ultramafic, mafic, intermediate and felsic colors. Dunite is an example of an ultramafic rock. The origin of intermediate rocks in large igneous provinces (LIPs) is unclear. Igneous rocks are classified by the minerals they contain. They include quartz syenite, quartz monzonite, and diorite, and their volcanic equivalents quartz trachyte, quartz latite, and andesite. Now that you understand igneous texture, color, composition, and whether an igneous rock is intrusive or extrusive, it is time to take that knowledge and apply it by identifying some igneous rocks. The limits of 52–65 wt.% SiO 2 set by Rosenbusch (1898) are widely accepted, although this range excludes a few extreme members of certain igneous families that otherwise lie within the intermediate range. If they erupt from volcanoes onto the surface as lava, they are called extrusive rocks.By contrast, Intrusive rocks are formed from magma that cools underground. If the intrusive rock cooled underground but near the surface, it is called subvolcanic or hypabyssal, and often has visible, but tiny mineral grains. The minerals in these rocks are the same as listed in … Ultramafic igneous rocks are also dark in color and contain higher amounts of the minerals found in mafic rocks. Intermediate rocks: Rocks composed mostly of hornblende and intermediate plagioclase feldspars make up the intermediate family of igneous rocks. Felsic: Derived from the words feldspar and silica to describe an igneous rock having abundant light-colored minerals such as quartz, feldspars, or muscovite.. Mafic: Derived from the words magnesium and ferric (Fe is the chemical symbol for iron) to describe an igneous rock having abundant dark-colored, magnesium- or iron-rich minerals such as biotite, pyroxene, or olivine. SUSD5 Student Igneous Rock Identification lab Igneous rocks are those that form via the process of melting and cooling. 3.4 Classification of Igneous Rock As has already been described, igneous rocks are classified into four categories: felsic, intermediate, mafic, and ultramafic, based on either their chemistry or their mineral composition. Intermediate igneous rocks contain 15-45% mafic mineral crystals. Mafic rocks have 45-52% silica content. Intermediate rocks (or andesitic) are those igneous rocks that contain between 52 and 63% silica. The main minerals in igneous rocks are hard, primary ones: feldspar, quartz, amphiboles, and pyroxenes (together called "dark minerals" by geologists), as well as olivine, along with the softer mineral mica. Can contain quartz and rare sanidine phenocrysts as well. The general and widely used term intermediate igneous rocks applies to igneous rocks with SiO 2 contents intermediate between those of acidic and basic igneous rocks. 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