Question

Which statement best explains why obsidian has a smooth glassy surface but basalt has a rough surface?

A. Obsidian is formed due to compaction and basalt is formed due to weathering.
B. Obsidian allows less crystal growth than basalt because it cools more rapidly than basalt.
C. Basalt is more easily eroded than obsidian because it is formed at a lower temperature than obsidian.
D. Basalt is formed from the erosion of sediments and obsidian is formed due to the metamorphosis of rocks.

Answer 1

a because it's the only one that made sense to me when i read it hoped this helped.

Answer 2

Option (B)

Step-by-step explanation:

Obsidian and basalt are both extrusive igneous rocks, that are formed when magma comes out to the surface of the earth. Basalt forms along the mid-oceanic ridge in the divergent plate motion, on the ocean floor, whereas obsidian forms in the continental areas from the eruptions of volcanoes.

As they come out to the surface, the minerals do not get enough time to form small and well-shaped crystals, because of the low temperature near the earth's surface. Due to this reason, basalt is comprised of coarse-grained crystals.

Obsidian is a rock that is comprised of no crystals. It solidifies at a much faster rate in comparison to basalt.

Thus, obsidian has a smooth glassy surface as forms no crystals and cools much rapidly than basalt.

Hence, the correct answer is option (B).