Hermosa Beach Rocks!
Posted by Jody on February 2, 2014
Here’s an interesting beach treasure found by Karen Williams on a recent visit to Hermosa Beach, California:
“Walking on the beach in Hermosa on Monday…”
“Found an interesting rock that appears to be 2 different kinds of rock fused together!”
“Beautiful weather in the 70’s and no one around!”
We asked our two very favorite geologists for their opinions on Karen’s beach treasure. This is what they told us:
“I think the rock’s finder is correct. This is two rocks fused together. It almost appears to be a quartzite (gray and white) fused together with a volcanic rock, perhaps a rhyolite, or andesite. One thing I can clearly make out is that the crystal sizes are much larger in the gray portion and much finer in the black portion. I think for this fusion to happen, the volcanic rock or ‘melt rock’ had to have ripped a piece of the ‘wall rock’ off without fully melting it. This means that the temperature of the melt rock was not high enough to fully melt the quartz-rich gray portion and instead incorporated it into its structure as an ‘inclusion’.”
Here is a reference in case you need something: http://www.minsocam.org/msa/collectors_corner/arc/tempmagmas.htm
~Ryan McLin (Geologist, Owner McLin Petrographics)
AND ~ Kristie McLin, Ph.D. says: “It looks like a metamorphosed bedding plane to me. Fine grained shaley rock (black) in contact with sand then becomes metamorphosed, changing to schist and quartzite.
We should say either could be the case, and it is hard to tell from a picture what it really is.”
Either way, it’s one great find!
Many, many thanks to Karen, Ryan, and Kristie. We just love to share!
What’s in your beach bag?