Building Stones MCQ with answer and solution

Concept

Sedimentary rocks form when sediments settle, get compacted and get cemented together.

Step-by-step solution

1. Basalt forms when lava cools fast, so it is igneous. 2. Pumice is volcanic glass full of gas holes, so it is igneous. 3. Sandstone is sand grains cemented by silica, lime or iron oxide, so it is sedimentary. 4. Flint is also a sedimentary silica rock (chert), but the standard expected answer is sandstone. 5. Answer is (C).

Explanation

Sandstone forms from sand grains that settle in layers and get cemented over time. So it is the standard example of a sedimentary rock. Basalt and pumice come from cooled lava, so they are igneous.

Why the other options are wrong

A: Basalt is an igneous (volcanic) rock. B: Flint is a silica rock found in chalk; it is technically sedimentary, but it is not the usual textbook example. D: Pumice is an igneous (volcanic) rock.

Shortcut

Sand, lime, clay type rocks (sandstone, limestone, shale) are sedimentary; lava rocks (basalt, pumice) are igneous.

Common mistake

Marking pumice as sedimentary because it is light and porous.