Question
A highly vesicular rock formed by solidification of viscous lava is
The correct answer is
pumice
The question asks to identify a rock characterized by being highly vesicular and formed from the solidification of viscous lava.
Vesicular Rock Formation
A highly vesicular rock contains numerous gas bubbles or vesicles, giving it a frothy appearance. This occurs when gas-rich, viscous lava erupts. As the lava rapidly cools and solidifies, the trapped gases expand and escape, leaving behind voids (vesicles).
Analyzing Rock Options
- Tuff: Formed from consolidated volcanic ash; may contain some vesicles but not typically described as highly vesicular.
- Obsidian: Volcanic glass formed from rapidly cooled lava; typically lacks vesicles, appearing dense and glassy.
- Volcanic breccia: Contains larger, angular fragments cemented together; vesicularity is not its defining characteristic.
- Pumice: A light-colored, frothy volcanic rock formed from highly viscous, gas-rich lava. It is highly vesicular, often containing so many vesicles that it floats on water.
Identifying the Correct Rock Type
Based on the definition, pumice is the rock that perfectly matches the description of being highly vesicular and formed from the solidification of viscous lava.
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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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