Spalted Walnut Back and Sides

Spalted Walnut is technically not a specific species of Walnut, Spalting is any form of wood coloration caused by fungi and can also occur even in living trees. 
Walnut (Junglas regia) is a relatively slow-growing tree, and is grown extensively for nut.  The wood is very high quality, and is used for furniture, rifle stocks, and musical instruments.  It is a porous wood, like the other walnuts, and is denser and heavier than black walnut.