Cummingtonite is a mineral that belongs to the amphibole group and consists of magnesium, magnesium, silicon, and oxygen. It is hard, shiny, and fibrous, with a dark green to black color. Some synonyms for cummingtonite include fibrous hornblende, grunerite, magnesiohornblende, and brown amphibole. These minerals have similar chemical compositions but slightly different crystal structures, which affect their physical properties. Fibrous hornblende, for example, is a more general term that encompasses a range of minerals with similar fibrous textures. Grunerite and magnesiohornblende are also types of amphibole minerals that can be confused with cummingtonite, especially when their crystal structures are not fully understood.