With the exception of the large quartz vein running through this rock, most people would find nothing of note to this rock.  However, under closer examination one can see hints of green through the rough, oxidized outside coating.  This piece presents a stark contrast between the raw, rough exterior and beautifully colored green interior.  

Rock type: Metamorphic basalt

There is a wide range of rock that can form metamorphosis of basalts.  Based on the green color, this rock is of oceanic descent and likely formed during subduction of an oceanic plate.  This particular specimen was invaded by quarts in multiple locations and directions presenting stark contrast between the dark green metamorphic basalt and white quartz.

Chemical composition: The exact composition of this rock is not known.  The origin is an ultra mafic oceanic basalt.