This cube from a breccia comes from a Washington River.  The chaotic mix of green and black shards in the white matrix paints a fascinating picture of a moment frozen in time.

Rock type: Breccia

Breccia is a type of clastic rock made up of particles trapped in a matrix.  The particles in breccias are angular and result from rocks and rock fragments that get trapped in a matrix after a landslide, eruption or cave collapse.  The angular shapes suggest that the rocks and rock fragments were trapped before they could be worn down and rounded.

Chemical composition: It is difficult to know the composition of this specimen.  It is likely the white mineral is silica.