Which of the following statements cannot be applied to the extrusive igneous rock obsidian?
A) It is composed of volcanic glass.
B) It possesses conchoidal fracture.
C) It is typically felsic in composition.
D) It cools very slowly.

Question

Which of the following statements cannot be applied to the extrusive igneous rock obsidian? 
A) It is composed of volcanic glass. 
B) It possesses conchoidal fracture. 
C) It is typically felsic in composition. 
D) It cools very slowly.

Quizplus · Accepted Answer

Obsidian is an extrusive igneous rock formed by the rapid cooling of lava. As a result, it cools very quickly and does not have time to crystalize, making it composed of volcanic glass. It also possesses conchoidal fracture, meaning it breaks into smooth, curved surfaces. Obsidian can be either felsic or mafic in composition, so statement C is not necessarily true. However, statement D is false as obsidian cools very quickly, not slowly.

Which of the Following Statements Cannot Be Applied to the Extrusive