Russula virescens

Common Name: None.
Description: Cap 5-12 cm across, convex then flattened; thick-fleshed; dull green to olive; surface breaking up into small, flattened patches, or granules like a mosaic. Stem 40-90 by 20-40 mm high and wide.
Habitat: in mixed woods, in particular beech. Found throughout northeastern North America.
Edible: Delicious.

Source: Mushrooms of North America by Roger Phillips.