Acanthite is composed mostly of silver, and is its most important ore. Acanthite and Argentite are usually grouped together in mineral guides as one mineral. However, they are scientifically recognized as two unique minerals, even though they are composed of the same substance. They only differ in crystal structure. As explained below in more detail, Argentite cannot exist at normal temperatures. Specimens labeled as Argentite are sometimes sold by dealers, however, these specimens are really Acanthite pseudomorphs after Argentite.
Acanthite is named for the Greek term akantha, which means "thorn", in allusion to it pointy crystal forms. Argentite is named for argentum, which is the Latin word used for silver.