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Identity HelpCalifornia rock id help

10th Oct 2016 17:09 UTCLauren Laur

08587280016040511326463.jpg
I have a lot of rocks that my sister found at a beach in California. Any ID help is appreciated. I'll try not to post too many at once. Thanks again. Here is one rock!



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05520410015660248604544.jpg

10th Oct 2016 18:04 UTCKeith Wood

There is very little within that rock to indicate what it is. However, based on the possible presence of chalcedonic quartz veins in a crackle breccia of very fine grained rock, I would guess that it started as a siliceous siltstone, or possibly fine rhyolite ash, and has since been silicified, brecciated, and infilled with quartz. Several other possibilities exist.

10th Oct 2016 20:34 UTCLauren Laur

ok thank you for your guess.

10th Oct 2016 21:44 UTCJohn Christian

It is a piece of brecciated Franciscan chert/jasper. What beach are they from? In northern California there is lots of Franciscan jasperized and brecciated chert that was created by subduction and metamorphism.

10th Oct 2016 22:47 UTCKeith Wood

That makes good sense.

10th Oct 2016 23:05 UTCLauren Laur

thanks.

I think it is from moonstone beach. There are some other rocks that she found that we are trying to figure out if they are jade or serpentine.

11th Oct 2016 04:05 UTCD. Peck

Lauren, check the hardness on the jade / serpentine. Jadeite and Nepheline are around 5.5 or 6. The Serpentine minerals are considerably softer.

11th Oct 2016 22:01 UTCLauren Laur

ok I will try. Thanks for the information don

13th Oct 2016 02:30 UTCPaul Brandes 🌟 Manager

I would agree that it appears to be a Franciscan Complex chert sample.

Very interesting rocks can be found in the Complex.....
 
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