Question

Which of the following rocks is not of volcanic origin?

• A. Obsidian
• B. Pumice
• C. Rhyolite
• D. Shale

Hint:

Remember: \[ \boxed{ \begin{aligned} \text{Obsidian} &\rightarrow \text{Volcanic} \text{Pumice} &\rightarrow \text{Volcanic} \text{Rhyolite} &\rightarrow \text{Volcanic} \text{Shale} &\rightarrow \text{Sedimentary} \end{aligned} } \]

Answer 1

The Correct Option is D

Concept: Volcanic (extrusive igneous) rocks are formed by the rapid cooling of lava at or near the Earth's surface. Shale, however, is a sedimentary rock formed by the compaction of fine clay and silt particles.

Step 1: Classify the given rocks.
• Obsidian $\rightarrow$ Volcanic igneous rock.
• Pumice $\rightarrow$ Volcanic igneous rock.
• Rhyolite $\rightarrow$ Extrusive igneous rock.
• Shale $\rightarrow$ Sedimentary rock.

Step 2: Identify the rock not of volcanic origin. Since shale is formed by deposition and compaction of sediments, \[ \boxed{\text{Shale is not of volcanic origin}.} \] Therefore, the correct option is \[ \boxed{(D)\;\text{Shale}.} \]