A volcanic saund grain seen unner the microscope, wi plane-polarised licht in the upper pictur, an cross polarised licht in the lswer pictur. Scale box is 0.25 mm.

Petrology (frae the Greek πέτρα, petra, "rock" an λόγος, logos, "study") is the branch o geology that studies the origin, composeetion, distribution an structur o rocks.