The correct option is Clay : Slate
Explanation
Metamorphism is the process by which pre-existing rocks (protoliths) undergo changes in mineralogy, texture, and chemical composition due to intense heat, pressure, and chemically active fluids. This process results in the formation of metamorphic rocks from igneous, sedimentary, or other metamorphic rocks.Analysis of Options:
- Option (a) is Correct: Clay (often in the form of shale), a sedimentary rock, transforms into Slate under low-grade regional metamorphism (high pressure). Slate is characterized by its ability to split into thin sheets (slaty cleavage).
- Option (b) is Incorrect: Limestone is a sedimentary rock that transforms into Marble upon exposure to heat and pressure. Granite is an intrusive igneous rock formed from the cooling of magma.
- Option (c) is Incorrect: Sandstone is a sedimentary rock that transforms into Quartzite through recrystallization. Marble is the metamorphic equivalent of limestone or dolomite.
- Option (d) is Incorrect: Coal is a sedimentary rock that transforms into Graphite or Diamond (or higher-grade coal like Anthracite) under extreme conditions. Basalt is an extrusive igneous rock formed from the rapid cooling of lava.
Key Takeaway: Important metamorphic transformations include: Limestone → Marble; Sandstone → Quartzite; Shale/Clay → Slate → Schist; Coal → Graphite.