Very smooth great for making tools. Very small crystals from unorganized ions. Characteristic of rapid cooling by either expulsion into the atmosphere or deep ocean. Aphanitic Texture Organized crystals indicator of slower rate of cooling, typical of the interior of lava flows. Still extremely fine grained small crystals only seen under a microscope Example is rhyolite.
Many aphanitic rocks contain vesicles or cavities resulting from trapped gas bubbles.
Phaneritic Texture Large enough crystals to be seen with the naked eye. Grains are all approximately equal in size. Slow cooling rate indicating that the origin must have been far below the Earth s surface not from volcanic eruptions. Pegmatites are very coarse grained and associated with water rich magmas. Two distinct grained sizes.