Building Stones MCQ with answer and solution

Concept

Igneous rock containing cavities

Formula

NONE

Step-by-step solution

1. Basalt is an extrusive igneous rock formed from lava that cools rapidly on the Earth's surface. 2. Dissolved gases escaping from the cooling lava form cavities or vesicles within the rock. 3. Consequently, basalt is an igneous rock rich in cavities (vesicles). Answer: B

Explanation

Basalt is an extrusive igneous rock that forms from lava erupting onto the Earth's surface, where trapped gas bubbles expand and become frozen in place as the lava cools quickly. These trapped gas pockets leave behind small voids or cavities known as vesicles within the rock matrix. Intrusive igneous rocks like granite and gabbro cool under high pressure underground and do not develop these gas cavities.

Why the other options are wrong

A) Granite is a dense, coarse-grained intrusive igneous rock without cavities. C) Gabbro is a plutonic igneous rock with a compact crystalline structure. D) Dolomite is a sedimentary rock formed from magnesium-rich carbonate minerals.

Shortcut

Basalt is an extrusive volcanic rock filled with cavities from escaping gas bubbles.

Common mistake

Confusing vesicular basalt with plutonic igneous rocks like granite that lack gas cavities.