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Xenoliths in Clear Creek Canyon, CO. These angular pieces were broken off when hot, molten rock intruded preexisting, crystallized, (black) rock, a process known as brecciated intrusion.  The angularity of the black pieces suggests that the intruding molten rock was not so hot--relative to the melting point of the dark rock-- otherwise the black pieces would have melted or at least become rounded.  Many black chunks in lighter colored granitic rock, for example, chicken heads in Yosemite granodiorite are rounded, indicating that they were melted somewhat by the enclosing magma.
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lin murphy
Jan 24, 2009
Xenoliths in Clear Creek Canyon, CO. These angular pieces were broken off when hot, molten rock intruded preexisting, crystallized, (black) rock, a process known as brecciated intrusion. The angularity of the black pieces suggests that the intruding molten rock was not so hot--relative to the melting point of the dark rock-- otherwise the black pieces would have melted or at least become rounded. Many black chunks in lighter colored granitic rock, for example, chicken heads in Yosemite granodiorite are rounded, indicating that they were melted somewhat by the enclosing magma.  

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