COARSE GRAINED TEXTURE (PHANERITIC), mineral grains easily visible (grains several mm in size or larger)
Phaneritic textured rocks are comprised of large crystals that are clearly visible to the eye with or without a hand lens or binocular microscope. The entire rock is made up of large crystals, which are generally 1/2 mm to several centimeters in size; no fine matrix material is present. This texture forms by slow cooling of magma deep underground in the plutonic environment.
A hand specimen of granite with phaneritic (coarse grained) texture. Principal minerals are Potassium Feldspar, Biotite Mica, and Quartz.
B) FINE GRAINED TEXTURE (APHANITIC), mineral grains smaller than 1mm (need hand lens or microscope to see minerals)
Aphanitic texture consists of small crystals that cannot be seen by the eye with or hand lens. The entire rock is made up of small crystals, which are generally less than 1/2 mm in size. This texture results from rapid cooling in volcanic or hypabyssal (shallow subsurface) environments.
A hand specimen of basalt with aphanitic (fine grained) texture. The dark color is due to abundant dark colored minerals (pyroxene, hornblende).