Epidote is a calcium, aluminum, and iron sorosilicate mineral with the ideal formula Ca₂Fe₃+Al₂(Si₂O₇)(SiO₄)O(OH). It crystallizes in the monoclinic system. It frequently occurs as well-formed crystals, commonly with a prismatic habit, with an elongation direction perpendicular to the plane of symmetry. They are almost always twinned. Their faces are usually striated in depth. Most of the mineral's characteristics, such as color, optical constants, and density, vary depending on the iron content. Its hardness is 6.5.