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The average density of basalt is 2.9 g/cm 3, compared, for example, to granite’s typical density of 2.7 g/cm 3. [16] The viscosity of basaltic magma is relatively low—around 10 4 to 10 5 cP—similar to the viscosity of ketchup, but that is still several orders of magnitude higher than the viscosity of water, which is about 1 cP). [17]
Granitic rock with more than 60% quartz, which is uncommon, is classified simply as quartz-rich granitoid or, if composed almost entirely of quartz, as quartzolite. [5] [6] [7] Granite in thin section, under cross-polarized light. True granites are further classified by the percentage of their total feldspar that is alkali feldspar.
Oceanic: 5 – 10 km (3 – 6 mi) thick [4] and composed primarily of denser, more mafic rocks, such as basalt, diabase, and gabbro. The average thickness of the crust is about 15 – 20 km (9 – 12 mi). [5] Because both the continental and oceanic crust are less dense than the mantle below, both types of crust "float" on the mantle.
A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it fractionally crystallizes to become a felsic magma, which is low in magnesium and iron and produces rhyolite or granite. Calc-alkaline rocks are rich in alkaline earths (magnesia and ...
The average density of the continental crust is about, 2.83 g/cm 3 (0.102 lb/cu in), [6] less dense than the ultramafic material that makes up the mantle, which has a density of around 3.3 g/cm 3 (0.12 lb/cu in). Continental crust is also less dense than oceanic crust, whose density is about 2.9 g/cm 3 (0.10 lb/cu in). At 25 to 70 km (16 to 43 ...
These rocks (diorite, andesite) are typically darker in colour than felsic rocks and somewhat more dense. Mafic rocks have a relatively low silica content and are composed mostly of pyroxenes, olivines and calcic plagioclase. These rocks (basalt, gabbro) are usually dark coloured, and have a higher density than felsic rocks. Ultramafic rock is ...
Acidic rock or acid rock refers to the chemical composition of igneous rocks that has 63% wt% SiO 2 content. [1] Rocks described as acidic usually contain more than 20% of free quartz. [2] Typical acidic rocks are granite or rhyolite. The term is used in chemical classification of igneous rock based on the content of silica (SiO 2).
The base of the sial is not a strict boundary, the sial grades into the denser rocks of the sima. The Conrad discontinuity has been proposed as the boundary, but little is known about it, and it doesn't seem to match the point of geochemical change. [8] Instead, the boundary has been arbitrarily set at a mean density of 2800 kg/m 3. [4]