ACTINOLITE VARIETY URALITE (AFTER DIOPSIDE), QUARTZ, CALUMET MINE, CHAFFEE COUNTY, COLORADO, USA (small cabinet)

 Actinolite is a silicate mineral belonging to the amphibole group, characterized by the chemical formula Ca2(Mg4.5–2.5Fe2+0.5–2.5)Si8O22(OH)2.

Its name originates from the Greek term aktis, which translates to "beam" or "ray," reflecting its fibrous structure.

Actinolite serves as an intermediate in a solid-solution series between magnesium-rich tremolite and iron-rich ferro-actinolite, allowing for the exchange of magnesium and iron ions within its crystal lattice.

This mineral is often found in metamorphic rocks, particularly in contact zones around cooled intrusive igneous formations, and results from the metamorphism of magnesium-rich limestones. Additionally, the term uralite is sometimes used to describe an alteration product of primary pyroxene that predominantly consists of actinolite, commonly found in metamorphosed gabbro or diabase, known as epidiorite.