Geo 730: March 16, Day 440: Colorful Coatings

I realized that despite the few photos I took at this rhyolite outcrop, Dana got some good ones too. The above photo, from this post, shows a pretty sample with its vesicles infilled with opal and agate. The agate tends to be a flat white or colorless and translucent at this location, and the opal tends to be vividly colorful- generally reddish to orange and yellow, but occasionally a dirty green. The texture of the opal below the tip of the hammer is called "botryoidal," an allusion to bunches of grapes. If you look at the full-sized image, you can see that spherulites are prevalent throughout the ground mass.

Photo by Dana Hunter, unmodified. August 19, 2011. FlashEarth Location.