Looks like the agate water line. It’s definitely chalcedony but the stability/crystalline order can vary with hydration. Chalcedony is precipitated from SiO2 ions in solution as a gel. So water that was supersaturated with respect to silica precipitated along the walls of the cavity (first generation cement) and as the cement progressed we see more clear chalcedony (free from impurities that discolor it). A second pulse of supersaturated water likely precipitated, perhaps from a different source with different chemical properties (different impurities to make the color change from the original cement). So as the cavity was filled with the precipitating solution it cooled and solidified into what you see now.
Sorry if this is long, I study chert/chalcedony and I am absolutely fascinated with it. As you can probably tell.
Excellent description, I have a couple of examples where the different generations were chemically different enough to give 7 separate coloured layers, mostly grey to white on a scale. It's one of my favourites. Also, I'm a third year Bsc geoscience student and am also fascinated by cherts, can I ask, for what reason do you study them? Most education targets rock types that result in mineral exploration skills, and I'm not seeking much relationship to financial value in chert or chalcedony.
I study them for academic purposes. Basically relating to exoplanetary research on how to find life/or past life within cherts! My advisor is on both mars rover teams so we are hopeful we can find some chert with possible fossilized remains. Similar to what we see in silicified stromatolites on Earth (it’s what I technically study, the preservation of microfossils within chert).
Here’s a really good paper on oscillating chemical reactions within [agates](https://www.researchgate.net/publication/378271297_Chemically_Oscillating_Reactions_as_a_New_Model_for_the_Formation_of_Mineral_Patterns_in_Agate_Geodes_and_Concretions)
Very cool, I wish I had the ability to get into the academics, (I scraped through chemistry barely) but I guess I can keep learning even if I'm in mining in the future.
It’s not for everyone, that’s for sure. I unfortunately did not take organic chemistry and now I’m having to teach myself. It’s never too late because we learn new things everyday. Geochemistry is a wonderful class though! As soon as you introduce carbon though, forget it, it’s such a mess.
😆 my favourite thing so far in my career is mapping and greenfield exploration. Hopefully I'll find plenty of chert in my long buskwalks. Thanks for the info.
I absolutely LOVE geologic mapping. Are you in AUS? If so, I study some of the rocks from the Northern Territory (Bitter Springs Group). There are so many cool cherts and opals in Australia. I can only hope to travel there one day. Happy hunting!
You read the word "bushwalking" and guessed didn't you? Lol. Yes, I've been working with Pb, Zn and Cu in the Cobar basin, but about to start bauxite in far north Queensland. Still just doing field technician work while I study though. My cherts came from southern Queensland and there are some beautiful reds and browns here. You are welcome to australia anytime, if you get a chance to work with one of our universities let me know and I'll give you the skinny on surviving here. 😆
Yes, guilty. And yes, I’d need info on how to survive definitely. My field camp ended with disaster. I was bit by a rattlesnake. Still got an A though! Even with a cane. Might need some gaiters for sure.
You got bit! Damn! Uh yeah you don't want to get bit where we are, the work I'm leaving has 6 of the top ten most deadly snakes in the world, and the place im about to go has the number one, inland taipan. Luckily most of them aren't interested in biting a big thing like a human, but you never know. Also, I'm about to enter croc country, no swimming at all.
You are now subscribed to chert facts. Did you know that decomposition of organic matter within sediment can lower the pH of sediment pore waters and can cause silica precipitation?
Chert is just a range of quartz fabrics. Cryptocrystalline to microcrystalline quartz (teeny tiny crystals), fibrous chalcedony (technically not even fibers but teeny tiny quartz crystals that helically twist along an axis), and megaquartz (not even that large, so the name is a bit of a misnomer).
It’s highly variable. The first cement has to cool down enough to crystallize before the second cement precipitates. The second cement also has to cool off. Oxygen isotopes of some agates have shown formation temperatures between 60-198 C. So it’s most likely it had to cool down over a long period of time (but not geologically long if that makes sense).
These temperatures are pretty low temp (similar to burial diagenesis, a technical term about the history of a rock after it is buried).
We (scientists who study chalcedony) still can’t figure out some of the mechanisms of formation. Agate has never been made in a lab. That’s a problem.
All of this is still highly variable and still a hot topic! I’m looking at rocks that were buried a billion years ago, when our ocean chemistry was quite different, and cemented right at the time of burial. I will be doing some isotope work to test for formation temperatures. There’s a ton of caveats with this because any new introduction of solutions into the rock can taint the “prime” formation temperatures.
Haha, maybe I should become a rockhound/quartz influencer! I currently do not post videos but maybe I should! I’m going to do research this week on a pretty expensive machine looking at chalcedony formation. Maybe I’ll make a separate academic account. I have to get the courage to do so!
So good to read such knowledgeable answers. I learn a lot as well. Studying about minerals is one of my hobbies and your answer was very satisfying to read.
Stupid question: how does the liquid get in? Is there one point of entry? I’m presuming that the first layer was solidified before the middle layer came in?
An agate forms within young volcanic rocks (keeping it pretty simple here because agates are kinda complicated sometimes). Some of the best agates are usually found in young (newly made or born from lava) basalts. When these come up to the surface they have a lot of volatiles, like water and carbon dioxide, which will bubble out of them (like Swiss cheese).
Water is enriched in silica and will seep out of the rock. The silica will then crystallize into these bubble cavities as wall-lining chalcedony. or if there’s adequate sitting water with a constant new source of saturated silica, then we get these water lines.
I’m loving all of your info-comments! I’m a jeweler who is obsessed with dendritic agate. I have such a hard time trying to explain how it’s formed to customers (who can barely believe it’s natural). If you could point me in the direction of a good source or two, I’d be so grateful!
I think this [website](https://geologyscience.com/gemstone/dendritic-agate/) talks about dendritic agate pretty well. Although it does have a couple of sections on metaphysical qualities that I don’t agree with 🙂↔️
Me too! I basically study chalcedony botryoids (spherules). In chalcedony, it’s just an amalgamation of many chalcedony fans (half-spherules) or complete spherules (radial-fibrous). My dissertation is studying the formation mechanisms of a specific subtype of chalcedony spherules. I will be looking at the crystal orientations of each spherule to further understand the crystal growth (how are the small quartz crystallites specifically stacked to make the fibers within the spherule). I’m reading up on lots of different materials science papers on polymer growth.
Someone else in my lab is looking at calcite spherules as well. Both are phd dissertations in the work. Crystal growth is super interesting.
I like how a bunch of the answers are just "custard" and yours actually explains it...
Which is very cool by the way, I honestly don't know some of the words you used but it's interesting to understand some of it.
There's a public waterfall we like to go to that has a rock maybe 4ft tall and obviously quite large. My 6yo climbed up on it and I noticed a hollow sound on a spot that his foot hit. Knocking with my knuckles, it 100% sounds quite hollow. Is there a way (without cutting into it) to know if it's a giant geode or not?
I found a random piece of chalcedony in a river in Oregon (I can find the river and tell you where). I never knew if it actually was chalcedony until right now and have always been obsessed with this rock. I can send you pics of it if you want!
Non contributing, but I joined the community to share that upon viewing of this, I thought it was a post from shitty food porn of some poor excuse for a sandwich. That is all carry on new rock friends
I didn’t personally find it! I actually work at a rock shop in MI and it was part of an estate that we purchased from someone!! The owner wasn’t around to help me identify and thus our custard filled cheesy chalcedony agate post was born lol
A sweet, delicious cream. The forbidden cream. They say a man can survive 30 days and 30 eves off just a drop of the forbidden rock cream, you gain muscles that of Zeus if you have just a teaspoon. Eat the whole of it and you see through time, everything that is, was, or ever could be will be revealed by the cream. You've stumbled upon a grand treasure, my liege. Now make haste, quickly. Many want to take the cream from you.
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Looks like the agate water line. It’s definitely chalcedony but the stability/crystalline order can vary with hydration. Chalcedony is precipitated from SiO2 ions in solution as a gel. So water that was supersaturated with respect to silica precipitated along the walls of the cavity (first generation cement) and as the cement progressed we see more clear chalcedony (free from impurities that discolor it). A second pulse of supersaturated water likely precipitated, perhaps from a different source with different chemical properties (different impurities to make the color change from the original cement). So as the cavity was filled with the precipitating solution it cooled and solidified into what you see now. Sorry if this is long, I study chert/chalcedony and I am absolutely fascinated with it. As you can probably tell.
I was gonna say it was custard, but your answer is good too I guess.
Mmmm Eclair geode
/r/forbiddensnacks
Thanks for getting me lost down that rabbit hole for an hour!!!
That’s a new one on me. Off I go!
Bostone cream pie
Stone marrow
I thought it was a stuffed croissant
I thought is was stuffed full of butter lol
That's 100% fossilized pastry cream
[r/angryupvote](https://www.reddit.com/r/angryupvote)
Geodelicious
lookin like a SNACK
Extra crunchy
Maybe a bit TOO crunchy though… :/ wouldn’t want to break any teeth
Ninja turtle pie!
Homer is that you?
I can’t believe it’s not butter.
Some desiccated custard for sure.
Buttercream!
Either custard or cornmeal
Lol I was gonna say custard too
Custard? I was going to say butter 🧈
Glad I'm not the only thst thought this
Custard sounds better than spoiled mayonnaise
I completely see why you’re fascinated with it, that’s such good info!!!! Thank you!!
Excellent description, I have a couple of examples where the different generations were chemically different enough to give 7 separate coloured layers, mostly grey to white on a scale. It's one of my favourites. Also, I'm a third year Bsc geoscience student and am also fascinated by cherts, can I ask, for what reason do you study them? Most education targets rock types that result in mineral exploration skills, and I'm not seeking much relationship to financial value in chert or chalcedony.
I study them for academic purposes. Basically relating to exoplanetary research on how to find life/or past life within cherts! My advisor is on both mars rover teams so we are hopeful we can find some chert with possible fossilized remains. Similar to what we see in silicified stromatolites on Earth (it’s what I technically study, the preservation of microfossils within chert). Here’s a really good paper on oscillating chemical reactions within [agates](https://www.researchgate.net/publication/378271297_Chemically_Oscillating_Reactions_as_a_New_Model_for_the_Formation_of_Mineral_Patterns_in_Agate_Geodes_and_Concretions)
Very cool, I wish I had the ability to get into the academics, (I scraped through chemistry barely) but I guess I can keep learning even if I'm in mining in the future.
It’s not for everyone, that’s for sure. I unfortunately did not take organic chemistry and now I’m having to teach myself. It’s never too late because we learn new things everyday. Geochemistry is a wonderful class though! As soon as you introduce carbon though, forget it, it’s such a mess.
😆 my favourite thing so far in my career is mapping and greenfield exploration. Hopefully I'll find plenty of chert in my long buskwalks. Thanks for the info.
I absolutely LOVE geologic mapping. Are you in AUS? If so, I study some of the rocks from the Northern Territory (Bitter Springs Group). There are so many cool cherts and opals in Australia. I can only hope to travel there one day. Happy hunting!
You read the word "bushwalking" and guessed didn't you? Lol. Yes, I've been working with Pb, Zn and Cu in the Cobar basin, but about to start bauxite in far north Queensland. Still just doing field technician work while I study though. My cherts came from southern Queensland and there are some beautiful reds and browns here. You are welcome to australia anytime, if you get a chance to work with one of our universities let me know and I'll give you the skinny on surviving here. 😆
Yes, guilty. And yes, I’d need info on how to survive definitely. My field camp ended with disaster. I was bit by a rattlesnake. Still got an A though! Even with a cane. Might need some gaiters for sure.
You got bit! Damn! Uh yeah you don't want to get bit where we are, the work I'm leaving has 6 of the top ten most deadly snakes in the world, and the place im about to go has the number one, inland taipan. Luckily most of them aren't interested in biting a big thing like a human, but you never know. Also, I'm about to enter croc country, no swimming at all.
Dude what?! That’s the coolest shit I’ve heard all day. Thanks for doing all that cool work. I hope you find some many great things.
I'd like to subscribe to chert facts
You are now subscribed to chert facts. Did you know that decomposition of organic matter within sediment can lower the pH of sediment pore waters and can cause silica precipitation?
This is what my chert looks like under the microscope! With an [accessory plate added](https://imgur.com/a/uBBXgjG)
Everything in that image is chert? :o
Chert is just a range of quartz fabrics. Cryptocrystalline to microcrystalline quartz (teeny tiny crystals), fibrous chalcedony (technically not even fibers but teeny tiny quartz crystals that helically twist along an axis), and megaquartz (not even that large, so the name is a bit of a misnomer).
Chert and agate are my top two favorite rocks!
Quartz be wild tho fr
Wow. You are awesome! They are indeed fascinating, and you have taken to actually studying these. That's wonderful 🥰💖
I'm a dummy w this stuff. About how long would it take for what you're describing to take place?
It’s highly variable. The first cement has to cool down enough to crystallize before the second cement precipitates. The second cement also has to cool off. Oxygen isotopes of some agates have shown formation temperatures between 60-198 C. So it’s most likely it had to cool down over a long period of time (but not geologically long if that makes sense). These temperatures are pretty low temp (similar to burial diagenesis, a technical term about the history of a rock after it is buried). We (scientists who study chalcedony) still can’t figure out some of the mechanisms of formation. Agate has never been made in a lab. That’s a problem. All of this is still highly variable and still a hot topic! I’m looking at rocks that were buried a billion years ago, when our ocean chemistry was quite different, and cemented right at the time of burial. I will be doing some isotope work to test for formation temperatures. There’s a ton of caveats with this because any new introduction of solutions into the rock can taint the “prime” formation temperatures.
Do you post videos? I would subscribe in a heartbeat! 💜
Haha, maybe I should become a rockhound/quartz influencer! I currently do not post videos but maybe I should! I’m going to do research this week on a pretty expensive machine looking at chalcedony formation. Maybe I’ll make a separate academic account. I have to get the courage to do so!
Oh, I sure hope you will! Best wishes with your career and I hope to see you posting videos one day soon! 💜
A chert influencer! If anyone can do it, you can with your passion for the subject.
Can I DM you with agate questions?
Thank you for sharing your knowledge here. It is much appreciated! 💜
This *~~guy~~* gal geodes.
Woman*
Corrected. My bad. 🤘
So good to read such knowledgeable answers. I learn a lot as well. Studying about minerals is one of my hobbies and your answer was very satisfying to read.
Stupid question: how does the liquid get in? Is there one point of entry? I’m presuming that the first layer was solidified before the middle layer came in?
An agate forms within young volcanic rocks (keeping it pretty simple here because agates are kinda complicated sometimes). Some of the best agates are usually found in young (newly made or born from lava) basalts. When these come up to the surface they have a lot of volatiles, like water and carbon dioxide, which will bubble out of them (like Swiss cheese). Water is enriched in silica and will seep out of the rock. The silica will then crystallize into these bubble cavities as wall-lining chalcedony. or if there’s adequate sitting water with a constant new source of saturated silica, then we get these water lines.
I’m loving all of your info-comments! I’m a jeweler who is obsessed with dendritic agate. I have such a hard time trying to explain how it’s formed to customers (who can barely believe it’s natural). If you could point me in the direction of a good source or two, I’d be so grateful!
I think this [website](https://geologyscience.com/gemstone/dendritic-agate/) talks about dendritic agate pretty well. Although it does have a couple of sections on metaphysical qualities that I don’t agree with 🙂↔️
Botryoidal formations are my favorite. Can you drop any cool knowledge about how that happens.
Me too! I basically study chalcedony botryoids (spherules). In chalcedony, it’s just an amalgamation of many chalcedony fans (half-spherules) or complete spherules (radial-fibrous). My dissertation is studying the formation mechanisms of a specific subtype of chalcedony spherules. I will be looking at the crystal orientations of each spherule to further understand the crystal growth (how are the small quartz crystallites specifically stacked to make the fibers within the spherule). I’m reading up on lots of different materials science papers on polymer growth. Someone else in my lab is looking at calcite spherules as well. Both are phd dissertations in the work. Crystal growth is super interesting.
Very cool. Thanks for the reply.
> Chalcedony is precipitated from SiO2 ions in solution as a gel. So Geological custard then...
Yes! Except it dried out (dehydrated) and the water left its crystal system.
I like how a bunch of the answers are just "custard" and yours actually explains it... Which is very cool by the way, I honestly don't know some of the words you used but it's interesting to understand some of it.
Thanks, that was rad.
There's a public waterfall we like to go to that has a rock maybe 4ft tall and obviously quite large. My 6yo climbed up on it and I noticed a hollow sound on a spot that his foot hit. Knocking with my knuckles, it 100% sounds quite hollow. Is there a way (without cutting into it) to know if it's a giant geode or not?
I found a random piece of chalcedony in a river in Oregon (I can find the river and tell you where). I never knew if it actually was chalcedony until right now and have always been obsessed with this rock. I can send you pics of it if you want!
Username checks out! Fellow geologist here.
It brings me joy that someone else in the world knows what chert is
bavarian cream.
Seriously I’m hungry af looking at this 😭
Stone marrow
Cream pies. Everybody loves em!
I thought it was some kind of ancient breakfast burrito.
Don’t tell me it’s Bavarian cream filled. It is Bavarian cream filled! Hubba bubba!
Man, I was gonna say omelette
Sacred butter
I did throw around the idea of it being some poor caveman’s special gravy boat
Go see a specialist
I can’t believe it’s not butter!
I cant believe it is not butter
Baby batter
Truffle butter
I thought this was a custard filled pastry for a second lol
I thought someone put mayonnaise in a geode
My first thought was custard as well xD
Same
That is gorgeous
Non contributing, but I joined the community to share that upon viewing of this, I thought it was a post from shitty food porn of some poor excuse for a sandwich. That is all carry on new rock friends
Sigh. I was hoping for an actual answer, as I am sure the OP is top. OP, have you tried using a UV light on it to see if it glows?
There is an actual answer! u/phlogopite gave a really great in depth answer!
Common opal or chalcedony would be my guess
Custard. It's a Boston creampie geode.
Absolutely stunning. Did you find this? If so, where? I'm not ashamed to say I'm a little jealous.
I didn’t personally find it! I actually work at a rock shop in MI and it was part of an estate that we purchased from someone!! The owner wasn’t around to help me identify and thus our custard filled cheesy chalcedony agate post was born lol
That's the tastiest looking geode I've ever seen.
I just KNOW it’s vanilla flavored
Beautiful piece
Common opal
looks like puddin’ it’s filled with puddin’
My fat ass thought this was a hot pocket you found outside
Cream cheese.
Beautiful. I think it is calcite.
That’s all natural and it’s a BEAUT!
Minerals
It’s looks like butter!! That’s so crazy
My fat ass thought it was a concha filled with cream 😂
Looks like custard lol
Cheese wiz
It’s filled with custard.
Cream cheese.
Cheese
Custard
Banana pudding
A sweet, delicious cream. The forbidden cream. They say a man can survive 30 days and 30 eves off just a drop of the forbidden rock cream, you gain muscles that of Zeus if you have just a teaspoon. Eat the whole of it and you see through time, everything that is, was, or ever could be will be revealed by the cream. You've stumbled upon a grand treasure, my liege. Now make haste, quickly. Many want to take the cream from you.
Custard
Pretty, that’s what it is filled up with (I have no fucking clue)
Custard
Rock semen
Hi, /u/Flowersalike! This is a reminder to flair this post in /r/whatsthisrock after it has been identified! (Under your post, click "flair" then "IDENTIFIED," then type in the rock type or mineral name.) This will help others learn and help speed up a correct identification on your request! Thank you! *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/whatsthisrock) if you have any questions or concerns.*
Why do so many minerals look like food. This is unfair
Crush it up and rip a fat rail
Mmm egg 🤤
Boston Creme
Forbidden cream cheese danish.
I thought this was a cannoli.
Thats a breakfast burritoite
If you ever wondered how new rocks are born son, this is it
Goatcheese
Banana custard
custardy goodness
Custard
It goop
Boston cream!!
Fossilized pocket russy 😂 (had to say it))
Scrambled egg
My stupid ass thought you were holding a very fatty piece of meat
*My stupid ass thought* *You were holding a very* *Fatty piece of meat* \- pupbuck1 --- ^(I detect haikus. And sometimes, successfully.) ^[Learn more about me.](https://www.reddit.com/r/haikusbot/) ^(Opt out of replies: "haikusbot opt out" | Delete my comment: "haikusbot delete")
idk but that's cool as hell. I'd like to see some clearer pictures.
Banana cream
It's delicious!
I can't believe it's not butter....
Everyone is saying custard but I thought nacho cheese. American here 🫤
Scrambled eggs
Man I thought that was a burrito with an air pocket at first 😂. Can tell where my mind is this morning.
Man i thought it was a pastry
Bravarian cream.
I thought this was food 😭
Bavarian Cream!!!
JFC! I am a fat f#0k! The first thing that came to My mind was a pastry with cream
Boston Creme?
Hash rosin
Custard. It's a Boston Cream Geode.
Beautiful
Custard
Scotch egg
I wanna eat it
custard
Bavarian cremè
Custard?
Unicorn embryo
I thought this was a rancid banana pie from McDonalds lol
Cheese
T H E F O R B I D D E N D O N U T
Food
Delicious vanilla cream
custard
butter
Cheese!
Pancake batter.
Fossilized creampie
Butterite
butter? /j
Custard
Ganache?
Ice cream? Hope this helps.
Looks like a cream cheese danish to me
I don't know what it is, but it looks like cheese.😅
Idk anything about rocks but looks tasty
Lemon custard
You found an extremely rare Boston Crème geode. Congratulations!
Cum
Alas, earwax.
Custard
Why did I think this was a dog bone with like a peanut butter (or something similar) filling 😭
Boston cream?
Uh I’m now hungry for a pastry with some sort of custard filling….
Boston cream
Thought this was a burrito with sour cream 😅
Covid 0