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_____ fragments commonly show normal grading in an ignimbrite.

A. Pumice
B. Obsidian
C. Andesite
D. Pyroclast

1 Answer

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Final answer:

The correct answer is Pumice. Pumice is a frothy-textured, felsic, extrusive igneous rock with no minerals. It has lots of empty spaces and is typically whitish or light grayish in color.

Step-by-step explanation:

The correct answer is Pumice. Pumice fragments commonly show normal grading in an ignimbrite. Pumice is a distinctively frothy-textured, felsic, extrusive igneous rock. Frothy textured igneous rocks have large numbers of tiny holes formed by the presence of many gas bubbles in the original volcanic lava. If cooling & solidification was completed before all the gas bubbles escaped to the lava surface, the result is a rock with lots of empty space (porosity). Pumice is actually a volcanic glass having a frothy texture. The solid portions of pumice are not crystalline. So, pumice has no minerals – it has the elemental chemistry of granite & rhyolite, but it doesn't have any minerals. Pumice is typically whitish, light grayish, or very light brown in color.

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