Which of the following rocks is not metamorphic

Analyze the question: You are asked to find the rock that is NOT metamorphic. Three of the options are metamorphic rocks, and one is not.

Explain the concept: Rocks fall into three main groups:

• Igneous rocks form from cooled magma or lava (e.g. granite, basalt).
• Sedimentary rocks form from compacted and cemented sediments (e.g. shale, sandstone, limestone).
• Metamorphic rocks form when existing rocks are changed by heat, pressure, or both, without melting (e.g. slate, schist, quartzite, marble, gneiss).

Step-by-step solution:

| Option | Rock | Type | Formed from | |---|---|---|---| | A | Shale | Sedimentary | Compacted clay and mud | | B | Schist | Metamorphic | Further metamorphism of slate or phyllite | | C | Quartzite | Metamorphic | Sandstone | | D | Slate | Metamorphic | Shale |

Shale is a sedimentary rock made of fine clay and mud particles compacted over time. When shale is subjected to heat and pressure, it changes into slate, which is metamorphic. So shale is the parent rock, not the metamorphic product.

Answer: The rock that is not metamorphic is A. Shale.

Tip: Remember the common change sequences:

• Shale → Slate → Schist → Gneiss
• Sandstone → Quartzite
• Limestone → Marble

The rock at the start of each chain (shale, sandstone, limestone) is sedimentary. The rocks it changes into are metamorphic.