Slate
Explanation
Metamorphism is the geological process where pre-existing rocks (protoliths) undergo physical and chemical changes due to exposure to intense heat, pressure, and chemically active fluids. This process alters the mineral composition and texture of the rock without melting it.Analysis of Rock Transformations:
- Marble is incorrect: Marble is a non-foliated metamorphic rock formed from the metamorphism of carbonate sedimentary rocks like Limestone or Dolostone.
- Slate is correct: Slate is a fine-grained, foliated metamorphic rock formed from the low-grade metamorphism of Shale or Clay. The pressure causes the clay minerals to align, resulting in slaty cleavage.
- Sandstone is incorrect: Sandstone is a sedimentary rock, not a metamorphic product of clay. When Sandstone is subjected to heat and pressure, it metamorphoses into Quartzite.
- Graphite is incorrect: Graphite is typically formed from the metamorphism of organic carbonaceous material or Coal.
Key Takeaway: Under heat and pressure, Clay (or Shale) transforms into Slate. If metamorphism continues with increasing intensity, the sequence is: Slate → Phyllite → Schist → Gneiss.