Wiktionary
hellyerite
n. (context mineral English) A monoclinic-prismatic light blue mineral containing carbon, hydrogen, nickel, and oxygen.
Wikipedia
Hellyerite
Hellyerite, NiCO·6(HO), is an hydrated nickel carbonate mineral. It is light blue to bright green in colour, has a hardness of 2.5, a vitreous luster, a white streak and crystallises in the monoclinic system. The crystal habit is as platy and mammillary encrustations on its matrix.