Dunite/olivine is one of my favorite rocks.  Dunite originates from the mantle and is a very dense igneous ultra-maffic rock that comes in a rich variety of green colors.  This piece is particularly interesting as it contains two different green colors nested together.  The cubic cut of the rock exposes the different colors in an unique and captivating way.

Rock type: Dunite, Igneous/Plutonic

Dunite is mostly olivine (~90+%) with other minerals such as chromite, magnetite, pyrope.  This piece contains chromite.

Olivine chemical composition: (Mg,Fe)2SiO4