Of the following given choices;
a. Softer parts of the rock melted in sunlight, leaving behind empty holes.
b. Contact with hard pebbles during cooling left dents in the rock.
c. Bubbles formed in the magma when it was still in liquid form.
d. Crystals embedded in the rock fell off due to friction in Earth’s
The answer is; C
This occurs especially in thick magma that has a high silica content. This magma has low viscosity and cools fast when exposed to the atmosphere. Also due to its high viscosity, it tends to trap its gases in bubbles (especially magma with high gaseous content such as sulfur dioxide) and when the magma cools into rock, the gasses escape leaving behind pores in the rock. An example of such as rock is the pumice rock.