Coarse-grained, crystals are large enough to be seen w/out a microscope, formed by slow cooling (intrusive).

Coarse-grained, crystals are large enough to be seen w/out a microscope, formed by slow cooling (intrusive).

• A. Phaneritic
• B. Aphanitic
• C. Glassy
• D. Porphyritic

Answer: (A)

In igneous rocks, crystal size reflects how quickly the rock cooled. Slow cooling beneath the surface gives crystals time to grow large, so the rock becomes coarse-grained and the crystals are visible to the naked eye. This texture is called phaneritic and is typical of intrusive (plutonic) rocks formed underground, like granite. If cooling were rapid on or near the surface, crystals would stay small and the rock would be aphanitic, with crystals that are too tiny to see without a microscope. Glassy textures arise from almost instant cooling, producing a rock with no structured crystals. Porphyritic rocks have two crystal sizes: large crystals (phenocrysts) set in a finer-grained matrix, indicating a two-stage cooling history rather than uniform slow cooling.

In igneous rocks, crystal size reflects how quickly the rock cooled. Slow cooling beneath the surface gives crystals time to grow large, so the rock becomes coarse-grained and the crystals are visible to the naked eye. This texture is called phaneritic and is typical of intrusive (plutonic) rocks formed underground, like granite.

If cooling were rapid on or near the surface, crystals would stay small and the rock would be aphanitic, with crystals that are too tiny to see without a microscope. Glassy textures arise from almost instant cooling, producing a rock with no structured crystals. Porphyritic rocks have two crystal sizes: large crystals (phenocrysts) set in a finer-grained matrix, indicating a two-stage cooling history rather than uniform slow cooling.