This cube from a breccia comes from a Washington River. The stark contrast of the dark breccia within the white quartz matrix makes for an interesting pattern that reminds me of animal skin.
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 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 quartz.