Question
Which one of the following is NOT a volcanic igneous rock?
The correct answer is
Syenite
Identifying Non-Volcanic Igneous Rock
Volcanic igneous rocks, also known as extrusive igneous rocks, form when molten magma erupts onto the Earth's surface (as lava) and cools quickly. Rocks like Dacite, Trachyte, and Komatiite are formed this way.
Rock Classification
The options provided are:
- Dacite: An extrusive igneous rock.
- Syenite: An intrusive igneous rock, meaning it forms from magma cooling slowly beneath the surface.
- Trachyte: An extrusive igneous rock.
- Komatiite: An ultramafic extrusive igneous rock.
Therefore, Syenite is the rock that does NOT fit the definition of a volcanic igneous rock because it is an intrusive (plutonic) rock.
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Important Questions from Igneous Petrology (Classification, Forms, Textures, Genesis)
- Match the rock types in Group-I with their most likely corresponding lithospheric / tectonic settings of formation in Group-II
Group-I Group-II P. Boninite 1. Continental anorogenic Q. Lamproite 2. Island-arc R. Phonolite 3. Continental collision S. Leucogranite 4. Intraplate oceanic - The mole percentages of SiO$_2$, Al$_2$O$_3$ and K$_2$O in a granitic rock are 84.21, 7.89 and 7.89, respectively. The molar proportion (in %) of K-feldspar in the rock is ________ [ round off to one decimal place]
- Which one of the following is a mafic volcanic rock?
Match the following igneous textures in Group-I with their definitions in Group-II.
Group-I
Group-II
P Vitrophyre 1 Alkali feldspar rimmed by plagioclase Q Rapakivi 2 Aggregate of radially arrayed, needle-like crystals of plagioclase with or without clinopyroxene R Ocelli 3 Sub-parallel skeletal, platy olivine and/or pyroxene S Spinifex 4 Large phenocrysts within a glassy matrix - Which one of the following statements about igneous rocks is CORRECT?
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