Friday, July 25, 2014

Geo 730: July 25, Day 571: Calcite Amygdules

At the southwest (downstream, toward the dam) end of the basalt outcrop near Green Peter Dam, there is what I would guess is a different flow of vesicular basalt. (It's unclear to me just how many individual flows are present in this outcrop.) The vesicles in this flow are less abundant, but much larger than elsewhere, and entirely filled with calcite. In addition, due to shearing in the flowing lava, they are typically pulled out into flattened teardrop-shaped lenses, reminiscent of almonds, the etymological source of the term "amygdule." There's a large one to the right of the upper yellow flower- the angular nature of the calcite cleavage obscures the form of the amygdule itself in that case. There's a smaller bit above and to the left of the same flower that shows a more representative section. There's a third, still smaller, and almost circular, amygdule between the two larger ones.

Photo unmodified. June 19, 2014. FlashEarth location.

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