a mineral of the chlorite group; one of the layered aluminosilicates.

The approximate chemical composition of chlinochlore is

(Mg, Fe)_4.75 Al,_1.25 [Al,_1.25 Si_2.75 O₁₀] (OH)₈

The ratios of magnesium to aluminum and aluminum to silicon vary considerably, although clinochlore is primarily a magnesium-aluminum chlorite. The low-iron variety of clinochlore is known as leichtenbergite (colorless). Clinochlore containing admixtures of chromium is called kotschubeite (pinkish-violet).

Clinochlore crystallizes in the monoclinic system, forming small pseudohexagonal plumose crystals with good cleavage. Most often, clinochlore forms microplumose aggregates. Its color ranges from dark gray-green to light olive-green. Clinochlore is transparent in the form of thin laminae. Its hardness on the mineralogical scale is 2–2.5; its density varies between 2,610 and 2,780 kg per cu m. It is a rock-forming mineral in chlorite shales and occurs in other metamorphic rocks as well (appearing as a result of changes in pyroxenes, amphiboles, garnets, ferromagnesian mica). Clinochlore also exists in contact-meta-somatic rocks, such as skarns, and in modified secondary rocks in hydrothermal lodes. Clinochlore is very widely distributed in nature.