Which rocks form directly from cooling magma or lava, with examples like granite and obsidian?

Which rocks form directly from cooling magma or lava, with examples like granite and obsidian?

• A. Igneous rocks
• B. Sedimentary rocks
• C. Metamorphic rocks
• D. Mineral

Answer: (A)

Rocks formed directly from cooling molten material are igneous rocks. When magma cools underground, crystals form and grow slowly, producing coarse-grained rocks like granite. If lava erupts to the surface and cools rapidly, it solidifies into glassy textures such as obsidian, with little to no crystal formation. This cooling-from-molten-rock idea distinguishes igneous rocks from sedimentary rocks, which come from fragments that are deposited and lithified, and from metamorphic rocks, which start as other rocks changed by heat and pressure. A mineral, meanwhile, is a single chemical substance and not a rock.

Rocks formed directly from cooling molten material are igneous rocks. When magma cools underground, crystals form and grow slowly, producing coarse-grained rocks like granite. If lava erupts to the surface and cools rapidly, it solidifies into glassy textures such as obsidian, with little to no crystal formation. This cooling-from-molten-rock idea distinguishes igneous rocks from sedimentary rocks, which come from fragments that are deposited and lithified, and from metamorphic rocks, which start as other rocks changed by heat and pressure. A mineral, meanwhile, is a single chemical substance and not a rock.