A borax bead heated in the oxidising flame with a trace of an unknown salt becomes violet (amethyst) when hot and cold. The metal is

Manganese gives an amethyst (violet) bead in the oxidising flame because of $\mathrm{Mn}(\mathrm{III})$ metaborate. Nickel gives a brown bead, cobalt a deep blue bead and chromium an emerald green bead.