Why does breccia have pieces with sharp corners?
1 min 49 s. The words are spoken and shown in the picture; the player can also show them as subtitles.
For the Earth and Space Sciences Regents. Topic: Sedimentary rocks, with the past questions on it.
What Dr. Mars says (the words of the video)
Why does BRETCH-ee-uh have pieces with sharp corners?
BRETCH-ee-uh is a rock made of angular pieces held together.
Angular means with sharp corners.
Sedimentary BRETCH-ee-uh can form from a rockfall below a cliff.
Gravity pulls broken rock down the steep cliff.
The pieces fall only a short way.
An earthquake can shake a cliff and start a rockfall.
The earthquake does not make the BRETCH-ee-uh itself.
Dr. Mars feels a corner of a fallen block.
It moved only a short way, so it was not rounded.
Later, sediment buries the pile.
Compaction and cementation turn the pile into BRETCH-ee-uh.
Weight squeezes the pile, and minerals from the water cement the pieces.
BRETCH-ee-uh also forms along a fault.
Movement along the fault crushes rock into angular pieces.
Dr. Mars taps the crushed rock with his hammer.
This is fault BRETCH-ee-uh.
In both places, the pieces were not carried far.
Pieces carried far in fast water become rounded.
That rock is conglomerate.
Check yourself! Which rock formed from pieces that moved only a short way: A or B?
Look at the corners of the pieces.
Answer: B! Its pieces still have sharp corners.
Like the block Dr. Mars felt below the cliff.
Dr. Mars. Free practice for the New York Earth and Space Sciences Regents.