BRECCIA (bresh ee uh) is a detrital sedimentary rock consisting of grains larger than sand (>2 mm) that have very angular particles. It is essentially a lithified rubble. Its geological significance is that it represents rock particles that have not been transported any appreciable distance. Transport of rock particles typically rounds off the sharp corners and in a breccia they are very angular (sharp). Commonly breccias are produced along fault zones where the rocks are ruptured and then cemented together in place. They may also form from the accumulation of rubble at the base of a cliff.
The difference between Breccia and Conglomerate is that a Breccia consists of angular fragments (rubble) while in a conglomerate the particles show obvious signs of wear (gravel).
Fault Gouge Breccia - Here the very angular particles are chert. Upon
faulting of the rocks the brittle chert is shattered. Fluids passing
through the zone of ruptured rocks along the fault can deposit minerals that act
as cement.
Caliche
Breccia - Near the base of a hill in Mayer, Arizona fragments of Basalt have
been cemented together by caliche. Note the high angularity of this
breccia. The caliche is a deposit of calcium carbonate and in Arizona's
desert areas it is a common constituent of the "C" soil horizon.
The following five images are of a fault gouge breccia from the Ray Mine. In the first set of pictures the left image is the "rough" rock. This is what the rock looks like in the mine. The cementing material is Copper. The image to its right is the back side of the breccia that has been cut with a diamond saw. It shows the angular nature of the rock fragments and how the Copper has leached into the pore spaces, crystallized and now holds the rock together.
In a similar manner the cementing agent of this Breccia is Chrysocolla. The left image show the rough rock and the right image show the back side that has been cut with a diamond saw. It is also from the Ray Mine, Arizona.
The following Breccia is another specimen from the Ray Mine.
