[9] Willemite is usually formed as an alteration of previously existing sphalerite ore bodies, and is usually associated with limestone.

[10] Crystals have the form of hexagonal prisms terminated by rhombohedral planes: there are distinct cleavages parallel to the prism-faces and to the base.

[11] It occurs in many places, but is best known from Arizona and the zinc, iron, manganese deposits at Franklin and Sterling Hill Mines in New Jersey.

It often occurs with red zincite (zinc oxide) and franklinite (Fe,Mn,Zn)(Fe,Mn)2O4 (an iron rich zinc mineral occurring in sharp black isometric octahedral crystals and masses).

When doped with manganese ions, it fluoresces with a broad white emission band.