Népouite is a rare nickel silicate mineral which has the apple green colour typical of such compounds. It was named by E Glasser in 1907 after the place where it was first described (the type locality), the Népoui Mine, Népoui, Nouméa Commune, Northern Province, New Caledonia. The ideal formula is Ni₃(Si₂O₅)(OH)₄, but most specimens contain some magnesium, and (Ni,Mg)₃(Si₂O₅)(OH)₄ is more realistic. There is a similar mineral called lizardite in which all the nickel is replaced by magnesium, formula Mg₃(Si₂O₅)(OH)₄. These two minerals form a series, that is to say intermediate compositions are possible, with varying proportions of nickel to magnesium.