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Chalcedony Filled Barnacles Of The Late Miocene Of California


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Thought I'd share my favorite (at least for a barnacle) find.

The locality, from which is this from, is very well known for being a place rockhounds have collected "agates" out of the nearby stream, but I was curious to their source, if nothing else to also find larger specimens than those washed and tumbled in the river. After hiking around the hills a few times over the course of several trips, I'd stumbled upon a small cliff with a ledge underneath and a very dramatic drop off. The face of the fallen cliff was where the "agates" were falling out of and the entire slope before the dangerous drop was littered with specimens from 1 cm in size to full barnacle clusters about 10-12" wide. Many pieces still had the porous barnacle shell attached and with chalcedony forming outside of the shells. From what I could tell, me and a few rabbits were the only ones who had visited the steep ledge.

I picked up a few pieces from this formation layer deposit and followed it into a neighboring valley where I found this gem on an adjacent trip, I was showing some friends the site.

The species of barnacle is described as :

Balanus gregarius (Conrad,. 1856)
Late Miocene Period
Santa Margarita Formation, Private Ranch, Santa Margarita, California, USA

Would this may be considered a cast, since none of the original shell is present and the crystals formed into the barnacles chambers?

The most common color chalcedony present in these specimens is a toss up between a semi-translucent white or light grey-blue.


Edited by AncientEarth
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Thanks Auspex, I guess this specimen takes a discerning collector to appreciate its beauty ;)

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Even the back-story is cool! I'd sure like to see this in rotating 3-D :wub:

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Very Nice Balanus! I was fooling around with some much less lackluster looking fossil relatives here in Florida yesterday. Thanks for showing--quite a find! Regards, Chris

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I would call it a mold (sort of) - if that is the cavity I am seeing where the barnacle's shell dissolved out of?

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  • 3 weeks later...

Thank you everyone, sorry for the delay in getting a reply back to you all. Been making use of the dry winter we are having here in California.

Wrangellian, to answer your question I am uploading a photo of the inside chambers of a specimen.


Also here are a couple that still maintain some of the outer barnacle shell. These are some of the nicer specimens, most are fairly small and loose chalcedony segments that I just pick up if they have nice color. I use the small bunk specimens as planter decorations. These were in my case until recently. The one with the golden center was just glowing when I found it on the hillside, sun hit it just right.



Plantguy, share a shot of some of the Balanus you find out in Florida, do they preserve with the same coloration as teeth and other bones?

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