The rare mineral , magnesium CaMgAsO4OH. It forms a solid solution series with the vanadium. Various transition metals substitute for magnesium and lead replaces calcium leading to a variety of similar minerals in the adelite - duftite group.
Adelite forms variably colored (blue, green, yellow and grey) crystals in the orthorhombic crystal system. The form is typically massive rating of 5 and a specific gravity of 3.73 to 3.79.
It was first described in 1891 from Värmland. Its name comes from the Greek word for indistinct.