Nickel sulfate hexahydrate appears as blue or emerald-green crystalline material. Toxic and carcinogenic. Two known phases. Alpha-form (blue tetragonal) converts to beta-form (green monoclinic) at 127.9°F. Becomes blue and opaque at room temperature. Odorless. Sweet astringent taste. Somewhat efflorescent. Greenish-yellow anhydrous salt is formed at 536°F. (NTP, 1992)
