Andesite porphyry
Extrusive igneous rock of intermediate composition.
Fine-grained purple/gray andesite matrix with phenocrysts (white and pink, coarse-grained crystals of feldspars that formed in the magma at depth, and were carried to the surface where the lava cooled quickly, preventing larger crystals to grow in the matrix).
Beach cobble from Carlsbad Beach, CA.Cobble is reworked from Eocene Scripps Formation and/or Pleistocene Bay Point Formation. Original source was Late Eocene gravel deposit associated the ancient Ballanas River system that drained from a volcanic region of Sonora, Mexico prior to the formation of the San Andreas fault system and opening of the Gulf of California starting in Miocene time. |
| https://gotbooks.miracosta.edu/rocks/igneous/6.html |
2/2/2021 |
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