Adelite

The rare mineral adelite, is a calcium, magnesium, arsenate with chemical formula CaMgAsO4OH. It forms a solid solution series with the vanadium-bearing mineral gottlobite. 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. It has a Mohs hardness rating of 5 and a specific gravity of 3.73 to 3.79.

It was first described in 1891 from Värmland, Sweden. Its name comes from the Greek word for indistinct.

Geologic occurrence
Adelite has been found in ore deposits in Algeria, Germany, Italy, Sweden and the US.