Which type of rock formations can have sills and laccoliths?

Which type of rock formations can have sills and laccoliths?

• A. Intrusive igneous
• B. Extrusive igneous
• C. Metamorphic
• D. Sedimentary

Answer: (A)

Sills and laccoliths form when magma forces its way into existing rock and crystallizes underground, creating intrusive igneous rock formations. A sill is a horizontal sheet that intrudes between layers of rock, while a laccolith is a lens-shaped intrusion that pushes the overlying rocks upward to form a dome. Because the magma cools slowly underground, the crystals have time to grow larger, giving a coarse texture typical of intrusive rocks. This differs from extrusive igneous rocks, which come from lava erupting onto the surface and cooling rapidly to form fine-grained textures. Metamorphic rocks arise from existing rocks altered by heat and pressure without melting, and sedimentary rocks form from deposition and cementation of minerals and fossils at or near the surface. So sills and laccoliths are best explained by the intrusive igneous process.

Sills and laccoliths form when magma forces its way into existing rock and crystallizes underground, creating intrusive igneous rock formations. A sill is a horizontal sheet that intrudes between layers of rock, while a laccolith is a lens-shaped intrusion that pushes the overlying rocks upward to form a dome. Because the magma cools slowly underground, the crystals have time to grow larger, giving a coarse texture typical of intrusive rocks.

This differs from extrusive igneous rocks, which come from lava erupting onto the surface and cooling rapidly to form fine-grained textures. Metamorphic rocks arise from existing rocks altered by heat and pressure without melting, and sedimentary rocks form from deposition and cementation of minerals and fossils at or near the surface. So sills and laccoliths are best explained by the intrusive igneous process.