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408rkgj

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Hello new member here, my name is Robert! :Wave: I found this site while searching google in an attempt to identify some beautiful items I came across recently while at the beach in san francisco. I understand most of you guys refer to yourself as amateurs, though reading a few forum topics before creating my account I was impressed with the amount of detailed information in regards to your studies and findings. That being said I must admit I am %110 amateur in my knowledge of fossils, different time periods, etc. So please forgive me if I seem to ask simple questions like I don't know what I am talking about, I am still learning. 

 

WELL, in regards to the piece I am hoping to learn about (please see attached image). I recently found it while I was at the beach in San Francisco area. It measures 2 and 3/4 inches wide, 2 inches tall, with a shallow depth of a 1/4 inch. My main question is...WHAT is it!? I've seen many sand dollar fossils, coral rock fossils, clam fossils recently on the beaches here, but I've only seen one like this. The milky white crescent shaped object that is offset to the right of the center of the stone, looks like a tiny shrimp or something (again :DOH:, please forgive my lack of knowledge). Also, the only thing I can relate the slightly irridecesent dark blue-ish streaks to are the inside of some of the mussel shells that I see on the beaches here, so maybe it is in relation to that...?

 

Again, I have no idea but I do speculate much as I've recently grew heavy in interest on the subject and those alike. It would be greatly appreciated if anyone has some pointers on or can possibly identify this, what I believe to be, fossil stone of some sort.

 

I have many photos of all the beautiful items I've recently collected, and needless to say, so many questions I wish to ask you all in regards to them. I am planning to post detailed images of them all in the My collections section but for some reason most of my pictures on my phone exceed the "Max total size of 3.95MB" in the image upload section so I am going to try and take some different pics that are "uploadable".

 

I would be more than happy to take new pics or zoom in closer on any specific area(s), if needed or necessary. Thank you all for your time 

20200326_181515.jpg

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53 minutes ago, 408rkgj said:

Sooooooo...just realized I should have posted this in a different section...:DOH:

 

Topic moved.  Welcome, Robert.  ;)

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Shellseeker

Robert,  I am not sure it is fossil.

Let me call on some of my TFF friends from your part of the world: @Spoons @caldigger @siteseer

 

Also Welcome to TFF, a real good place for fossil hunters....

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Welcome to the forum. That is a really neat looking rock, I’m just not sure that it contains any fossils. It’s possible that there are some heavily recrystalized fossils in there, but I think it is all geological. The black pieces are most intriguing to me, some interesting shapes that I’m not sure what they are. 

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22 hours ago, ClearLake said:

Welcome to the forum. That is a really neat looking rock, I’m just not sure that it contains any fossils. It’s possible that there are some heavily recrystalized fossils in there, but I think it is all geological. The black pieces are most intriguing to me, some interesting shapes that I’m not sure what they are. 

Hi! Welcome to the Forum from Humboldt!
 

This specimen looks upon first glance to be typical fossiliferous sediment that I might come across on a typical day however upon further inspection it’s appears to be metamorphosed.  
 
This would make sense because if my memory serves me right, the rocks around San Francisco are highly altered deposits of the Fransician Complex. As Clearlake said the black bits have me confused and definitely intrigued. I wonder if it isn’t some metamorphosed graywacke and the black spots aren’t just recrystallized lithic inclusions in the protolith. 
 
I am curious about how other members will respond.

 

Unfortunately It’s late at night, and I’m responding to this from bed. I’ll post some picture of what kind of sediments I’m talking about tomorrow.

 

-Nick

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DPS Ammonite

Welcome to the Forum. Check out the Northern California Geological Society that meets in Orinda.
 

This might be a piece of shell rich sandstone from the Pliocene/Pleistocene Merced Formation which occurs along the beach from southern-most San Francisco to the Daly City area in San Mateo County. It also could be an exotic piece brought in to build a nearly destroyed roadway along the sea cliffs close to the San Andreas Fault. I remember seeing exotic rocks at the beach in Daly City including petrified wood.
 

This is not a piece of Franciscan Complex rock as fossils in the Complex are extremely rare and often scientifically valuable.

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I have never been to California, although I'd love to get there some day, so I've never had any stone from San Francisco beaches in my hands and can only go by the photos. It does however look like a sedimentary rock with interspersed shell material to me as DPS is suggesting. I think your best bet to learn more about it and your other finds is to contact the NCGS that DPS mentioned. Of course feel free to post as many of your finds as you like under Fossil Id or Hunting Trips. I would suggest you save your best finds for My Collections. By the way, there are a good number of gratis programs for reducing the size of your photos before you post them. And welcome to the forum!

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Welcome to the forum! You've come to the right place. ;) We may not be able to answer all questions but we do have a great diversity of knowledge in the form of members willing to answer questions.

 

Many of our members would have stopped to pick up such a curious rock. My first thought would have been a conglomerate rock composed of shell fragments in a darker matrix but I'm not really seeing signs that point to a biological origin. I think it is probably a really cool rock of geologic origin with interesting veins of minerals that look to have been warped and twisted over time. We see lots of shell-hash rock here in Florida but I have no experience of the geology of northern California so I can't give more than an uneducated opinion. We have a member who we like to call upon for geology/mineralogy questions @ynot and perhaps when Tony sees this he might chime in. He's in your part of the county so possibly that will help.

 

If you don't get a reasonably definitive answer from us here, I encourage you to seek out either local rock/gem/mineral clubs in your area or local museums that might have a geologist on staff. If you do get a "professional" diagnosis of what this rock truly is, we'd appreciate you letting us know here. Past posts are a record of knowledge gained and provide a great resource for future visitors to the forum.

 

Regarding picture posting size limits--smart phones will allow you to adjust image size without the need for photo editing software. You should be able to email yourself an image and should be able to specify the quality/size of the image when attaching it. You should then be able to post this reduced size image here on the forum. There is a size limit per post and another way around is to reply to your own post (as you did above) to provide additional imagery.

 

 

Cheers.

 

-Ken

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10 hours ago, DPS Ammonite said:

This is not a piece of Franciscan Complex rock as fossils in the Complex are extremely rare and often scientifically valuable.

I apologize for not being more clear. As I said in my earlier post, I was very tired at the time of writing. I didn’t mean to insinuate that this rock came from the Fransician Complex, but rather that the rocks around San Francisco are highly deformed, and as such may provide a reasonable explanation as to why it seems metamorphosed to me. I was unsure of formation but what award that it wasn’t Franscian in origin. 
 

Thank you for clearing up this discrepancy for other members. I do not want to provide or spread mis-information.

 

I still feel this is fossiliferous matrix. Attached below are some examples from the Miocene/Pliocene price creek formation. 

FB5A8791-C933-4B9F-8F8A-278CD8B930E8.jpeg

4965F2FC-EBE2-46DB-81F5-2FA39D38912F.jpeg

2F6F2677-6D27-4BBB-BD53-37A39CB79888.jpeg
^Cross section showing Scutellaster major

4E8B0212-E714-4B11-ABA3-09F51629D8E9.jpeg
 

What I’m suggesting is that OP has a slightly more metamorphosed version of this type of sediment. 
 

I think I might even see a sand dollar in there.

7D46D638-7784-4337-8E9C-93D41ED1289C.jpeg

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Woah, what a pleasant surprise to wake up to all the constructive information in all your responses, thank you all. The last picture that Spoons posted in his reply seems to closely resemble the piece I have in question, or vice versa. I am still perplexed at what that white colored half moon looking object in the middle of the rock is. I have a few other smaller stones I found that has the same looking imprint. It may just be a coincidence that it has a shape like that, initially I believed it may have been some sort of living creature at one point because the same imprint seems to show on these other small stones I found...? Again I have no professional ideas, just speculation. I posted a pic of the stones containing that same shape below. Also thank you for the Merced formation info! Super interesting stuff, I just started reading more about it. Thornton beach in Daly city is one of my favorites I an actuallyhesding down there in a few hours! I usually hit Thornton beach in daly city and then walk south down the shoreline at low tide, it seems to be a hotspot for cool stuff like this. 

 

Also in response to DPS Ammonite: the old nearly destroyed road near the shoreline (if we are referring to the same one) is still there and visible from where I go to at Thornton beach. I had a local point it out to me one day and I have been dying to go up there and explore BUT it is extremely dangerous as it sits on top of a huge cliff known for rock slides so I have been hesitant.

 

Anyway the pic below shows that same crescent like shape I was questioning, anybody know if those shapes shown in each rock are related or just coincidence? Thank you all again, love this website! 

20200327_102002.jpg

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Your crescent shape on the right is probably an eroded gastropod.

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DPS Ammonite

Here is an article about a nearby section of Merced Fm along with a checklist of fossils.

 

https://pdfs.semanticscholar.org/f6ad/25c1f80947c2311912d8d8b068c5849c6aea.pdf

 

@408rkgj Look for a black layer of peat in the Merced at the beach in Daly City. I once found a small iridescent beetle in it. Nearby you will find imprints of marsh plants including bullrush and their roots.

 

The attached fossil is a cross section of a coiled gastropod.

0021E04E-E819-49F7-B7A2-8A4A5E6AD09B.jpeg

751E3DC3-6F96-42AC-B7A9-C954A1118114.jpeg

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Neat Gastropod! :dinothumb: They’re my favorite.

Ill have to check some of those beaches next time I go down and visit my sisters.

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Bad @##!! Thank you guys that's exactly what I was looking to identify :fistbump: and then you as well for that list, that will most certainly come in handy for me, much respect! 

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I agree that the first piece is shell pieces in sandstone. It is a low grade metamorphic rock and the shell is recrystallized. Not sure about the black spots.

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Thanks, Tony! Metamorphosed shell hash seems to be our best ID for this interesting piece.

 

 

Cheers.

 

-Ken

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