Stibarsen is a natural mixture of the elements arsenic and antimony, and its name is a combination of stibium (which is the latin name for antimony), and arsenic. Allemontite, another name for this mineral, is usually used to describe the ratio percentage of antimony to arsenic. Allemontite is named after Allemont, France, an important locality for this mineral.
Any mixture of arsenic and antimony that constitutes 80% or more of one element is classified as that element. For example, a specimen with a ratio of 80% arsenic and 20% antimony is recognized as Arsenic. Conversely, a specimen with 80% antimony and 20% arsenic is recognized as Antimony. Any combination with less than 80% of either arsenic or antimony is classified as Stibarsen.