The Rock - BRECCIA
- Sedimentary Rock Type: Clastic
Related to: Sandstone
Texture: Angular pebble to cobble sized grains
sometimes in a finer grained matrix
Origins: Debris flows, fault zones, cryptolithic
explosion events and impact site deposits
Common Minerals: Quartz, feldspars,
Uses: Building material, decorative stones, tiles,
tombstones, monuments, jewelry, aquifers, natural gas and petroleum
Breccias are a relatively common clastic
sedimentary rock. They
form in many different violent situations where host rocks are broken and
not transported far from their source. These situations include any scenario
in which rocks can be broken and re-accumulate to form the angular sediment.
Landslides, fault zones, cryptolithic explosion events and impact craters
can produce breccias. Landslides or debris flows can occur on continental
shelves, on the sides of mountains or in karst environments such as sink
holes or collapsed caves. In fault zones, where rocks or even continents
slide past each other, breccia zones can be created that can vary from inches
across to tens of meters across. Cryptolithic explosions are subterranean
explosions that can send rocks flying into the air and the debris that falls
back to Earth forms brecciated deposits. Meteorite impact craters can form
breccias as the meteor impacts the Earth and the debris is strewn across
the country side or back into the crater. However breccias are formed, it
usually is an exciting event!The sediment from which it forms is composed of angular pebble to cobble
sized fragments often dispersed in a finer matrix. The only difference between
breccias and conglomerates is the roundness of the grains. In
the grains are rounded and usually indicate that they have been transported
or worked more than the angular grains found in breccias. Distinguishing
between breccias and conglomerates is usually very easy as the grains are
mostly large enough to see with the unaided eye. If the rock has a smaller
grain size (< 2.0mm) which is almost too small to see, then the rock is
Like sandstone and conglomerates, breccias are cemented by various minerals.
Normal cementing agents include
When the sediment is first deposited there are lots of open spaces or pores.
Cement can affect the amount of pore space that is left in a rock as it solidifies.
Breccias usually have significant pore space and they are generally a good
rock to act as a reservoir for ground water, natural gas and petroleum.
Breccias have very unique angular textures and are prized as ornamental rocks
for buildings, monuments, grave stones, tiles and many other ornamental uses.
They have been used by people for centuries for many ornamental uses and
some breccias are even considered to be semi-precious and have found uses
Breccia is a term that has been applied to non-sedimentary rocks of igneous
origin too. At times there are situations in the formation of igneous rocks
that produce angular fragments that solidify with a breccia-like texture.
These rocks are sometimes referred to as breccia, but are not sedimentary
and it is probably better to use the term as an adjective such as a brecciated
gabbro for example instead of calling the rock a breccia.