Nephrite Jade is one of the two species of mineral commonly referred to as Jade. The other is Jadeite.
Nephrite Jade is significantly more common than Jadeite. It typically occurs as a translucent mineral with black and darker inclusions, giving it a mottled effect. There can be a considerable variety of colours, from very light green to a darker green, almost black. The translucency does vary pretty widely, too.