Unpolished rice with a black bran, usually not glutinous, so it stays firmer than 紫米. It is soaked for a few hours, then cooked with other grains in porridge or mixed into white rice, which it dyes purple.
Black rice porridge is more nutritious than white rice.
Tips
culture
Also called 贡米 ('tribute rice') because it was once sent as tribute to the emperor; in English it is sold as 'forbidden rice'. Cooking turns it deep purple. Common in northern porridges and the Cantonese dessert 黑米露.