I just love your channel! Being a new rockhound starting my rock journey this spring 2024. I have watched almost all of your videos, and I have learned SO much from them. I still rewatch and learn more every time I do. Thank you so much for sharing them.
Thank-you. Haven't sat in a college classroom in decades so this was a real treat. I love learning new things in the sciences, esp. physics, geophysics-volcanology in particular. This was great! I had never really seen the different grades of coal before, up close-very informative! I especially love your walking lectures. Please keep them coming.
I never realized that coal was so soft. That Anthracite doesn't look soft, but you showed that it is basically charcoal, or Carbon. My son has found Chert arrowheads here in New Mexico along the old trails along the Rio Grande river. Excellent presentation Shawn.
The husband and I started rockhounding on the beaches of all the Great Lakes a few years back and still find identifying our rocks/minerals so confusing. I’m learning so much from your channel! I love it! Thank you Professor! 👍🏼
Hi, I'm in Northern WI and go up to Lake superior. I too found rock identification very confusing. These videos are amazing. So happy I found this channel. Happy rockhounding!
I love chert. When I was a kid, teachers showed us how to work chert. This was before there was anything worth watching on TV, so we put quite a bit of time into learning to work chert and got quite good at it.
I've come across chert when I've been looking for fossiliferous limestone. I used to think I lived in a geologically boring part of the world, but this series has maybe shifted my outlook. The glaciers deposited so many different rock types, and I was kind of blind to that. Next time I'm oot and aboot, I'm going to have a different eye. Thanks Professor!
This lesson has been especially pleasing as I find both Chert ( Flint ) and Coal truely interesting and quite fascinating how biochemical processes make rock. Nice example of chert in limestone and the Anthracite was a new one to me. So a simple piece of bituminious Coal, even the youngest must still be about 50 Ma !
Great video, I’ve really enjoyed the sedimentary vids, being from the WV-KY area that’s all I ever saw as a kid, I still remember being shocked when a 10 year old me learned that coal isn’t found in about every rock cut like here in East KY-WV. I think that’s when my interest in geology started
Great and timely information! I just returned from a birding tour in So Texas, and brought back samples from Star Base, Boca Chica, Rio Grand, (and at Indian Point there was a whole jetty of limestone)! Thank you! 🥰
When I was born, the house we lived in was heated with coal. And now, 64 years later, the only coal used here is probably by hobbyist blacksmiths. it leaves a mark, though. Last summer, I was investigating an upturned tree along the local river. The dirt pulled up in the tree roots gives a picture of what's under the ground. Sure enough, I found small bits of coal. I'm guessing industry and home owners probably dumped their ash into the river, and these were small unburned bits that got deposited on the river banks during annual spring floods. If coal was ever used where you live, you'll probably find traces. Old houses will have a small "window" in the foundation. That's the old coal chute door. Dig around one, you'll probably find nickel or quarter sized bits of coal.
Very informative presentation. It was great seeing close up example of the rock. I have been surprise to find that we had coal mines not far from Portland. This was also tied in with the gas fields that are still active today. It speaks to a way different eco system then we have now.
Best teaching geology videos on the net! Thank you! I appreciate you, your knowledge and for sharing your years of studying. This is exactly the kind of videos I have been searching for.
I've run into a similar breccia type material here in SW PA/WV--Along the Cheat River. It's definitely a conglomerate found in conjunction with limestone. I think the local Indians quarried it for their lithic material needs. I find it, oftentimes, quite near artifacts as if they sought it out for a specific purpose. Enjoying your videos! Way more than actually attending a college class. As a 47 year old Iraq veteran I can't deal with the students like I once could. God bless them.
I learned that many of my backyard rocks are cherts. Some have that smooth surface texture, with a brown mustard or chocolate color, and others have rougher, gray, tan, etc surfaces. Some polish up to look like tiger's eye. It's fun to discover what lies beneath the surfaces of common rocks. Also, great shirt! That's a good color for you. Thank you.
Thanks for sharing so much information in all of your videos. Learning from your videos definitely adds another fascinating layer to my collection of rocks!
Very nice video. I love the descriptions that taught me how to tell the difference between the different types. I'm very familiar with getting cut by a piece of obsidian... not fun... was not expected... and I had a sliver of it that I had to dig out of my finger.
wasnt sure if a certain piece i had was coal or not, and your technique of putting pressure on it was the key. heard a light cracking sound, then i knew:)
Glad I found your channel, I've always had some interest in rocks! Thanks for the pronunciation of "chalcedony" -- I was pronouncing it to myself as rhyming with "alimony"
NOTHING rhymes pleasantly with alimony. Child support, YES! Contending hate-greed , though DOES rhyme with alimony, in case you are a lyricist, inclined to odious odes..
Here in East Texas some commercial parking lots have treed islands using rounded Arkansas river rock as ground cover. Most of it appears to be chert, marble and other hard stuff that's often banded or a banded conglomerate. I kept one that's red chert covered with small white dots and fine whites that go in all directions and slightly wider white lines that cross each other at right angles. You an play Tic Tac Toe on it! The rocks came off the ancient Ouachita Mountains so there's no telling how old those may be.
I never knew peat was a rock! It is interesting to see the different ways that academics and industry differ. Industrial coal usually starts with Lignite and goes up from there to sub-bituminous, bituminous, and anthracite. In coals value for heat production is the highest is the best grades of bituminous because it has a substantial amount of heat from the hydrocarbon content that is lost as it becomes anthracite. Another distinction is metallurgical grade coal which is bituminous coal with low ash content and low amounts of impurities that are a problem to steel production. This coal is common in western Pennsylvania and is the reason Pittsburgh became a center of steel production. Anthracite was favored for it's low amount of soot when it burned and that made it's primary usage for heating in urban areas. For a long time the British navy had first right to anthracite coal in the UK because it didn't leave tell tale smoke trails behind their ships.
Professor, what factors cause segregation of silicate organism detritus from calcareous organism detritus? Why aren't silica and lime mixed together in rocks originating from seafloor oozes? I've always wondered what determines where radiolarian chert forms versus where limestone forms.
According to the USGS peat is a precursor to coal and there is lignite (mined here in Texas), subbituminous, bituminous and anthracite. The lignite mine associated with a power plant had piles of petrified wood that came out of the mine.
Just watched this video, I am from quebec canada. I found rocks on a riverbed while fishing, I had beleived that they were coal.they are a pretty solide black rock ,dull in colour and you can write with them. my research show me that they were coal. are they possibly something else. I know coal is not usaully found in river beds but there are lots of mountains around.
Learned a lot from this. I had no idea that chert had biochemical origins. What happens when the metamorphism of coal goes beyond anthracite? Thank you!
There's also an Oregon coastal coal bed - Eocene age. It was used for transport and heating in the latter half of 1800s.See the Coos Bay- Coquille formation.
Hi Dr. Willsey. Totally unrelated question here (can’t find a way to message you about it). In Southern California near the town of Boron, there are some beautifully colored mountains (when they’re mined) that look just like the rhyolite mountains in Landmannalaugar in Iceland. Are they rhyolite or are they something else? Thanks!
Interesting, I didn't know about coal in KS. My grandfather was from Central Kansas. There are stories in the family about going to the chalk hills. I had also heard about chert being found in KS. This is making the geology of the plains more interesting to me.
Love this rock identification stuff. It's so cool. As you probably know, i'm a new comer to your videos, as well. I wanna see all of them. I hope to have this question answered....At what degree of metamorphism, heat and pressure, does coal become anthracite?
Great you have samples of flint from Dover UK. It was used widely for houses and churches. I've always wondered why they were deposited in layers, (horizontal bands). Anyone got any thoughts/ ideas why this is? I'm enjoying rediscovering rocks again. Thanks!
so why is flint associated with sparks? I looked it up: "When struck against steel, a flint edge produces sparks. The hard flint edge shaves off a particle of the steel that exposes iron, which reacts with oxygen from the atmosphere and can ignite the proper tinder." So, it seems that in order to chip off a small piece of iron, you need a very sharp edge. that's why the flint is needed.
Very few people know that coal has pyrites. I worked in a coal burning power plant for 23 years. They use pulverizers to crush the coal into a powder they blow into the boiler. There is a chute at the bottom of each pulverizer for the pyrites to fall out, because they're harder than the coal. I've seen where a lot of gold miners find pyrite and they call it fool's gold. I wouldn't think that gold would be located with coal. Is there a connection or it is coincidence that pyrite is found with gold and coal?
If I'm not mistaken pyrite mainly forms under anoxic conditions. Which tends to be the condition under which plant remains become coal. So there is indeed a connection.
This is interesting to me. When you mentioned that, I realized that all the times I have found pyrite is in Central Washington, in Cle Elum/Rosslyn area and also the nearby Blewett Pass area. In the first area, there were coal mines. In the Blewett Pass area, there were and still to a limited extent gold mining. These areas are actually fairly close to each other. In addition, the rocks removed to get to the coal are layers of red sedimentary rocks that are packed full of plant fossils. Which to me makes complete sense. I am only a lay person learning a bit more geology. My mother was from Illinois. When I was a child, she told me about the types of coal. She was telling me a little about mining as we drove through West Virginia. She had also grown up in a house with a coal furnace. The first coal I saw was waist left in the coal bin room of the basement of that house.
@@Anne5440_ I had heard about coal in WA, but it was my understanding there wasn't that much of it or it was hard to get. I know there is gold around Liberty. I visited that area in Sept. of 2021. When I was working in a coal powered power plant, we got half of our coal from IL. Of course, in the power business, cost is a big factor in where they buy the coal, plus the sulfur content and hardness, and other factors are considered. But that wasn't my department. I just burned it to boil water. 😀
@@7inrain I can see that, as we got tons of pyrites from coal in a shift in the powerhouse. But why is it around gold? Seems like two very different sources.
@@GregInEastTennessee _"But why is it around gold?"_ I have no clue why that is. Guess that has to be answered by Professor Willsey. Funnily enough I have one piece of limestone consisting of fossilized corals on my bookshelf. And it both has tiny crystals of pyrite and a few microscopically small flakes of gold on it. So what you experienced I did as well.
Had to check it twice: you basically stated that obsidian is a chert. I do not believe that obsidian is classified as a sedimentary rock. Rather obsidian is an igneous rock produced from lava flow which contains lighter elements such as Si, O, Al, Al, Na and K. Also , obsidian has a shiny glassy sheen, unlike the Cherts which have a softer duller sheen. Just saying.
I did not state this. I know the difference between chert and obsidian in terms of classification. Also, note that I have a video on Igneous Rocks featuring obsidian: th-cam.com/video/xX6YGpk3DWk/w-d-xo.html In the video you mention (with chert), when discussing conchoidal fracture, I state (at 2:07 mark): "this is what made chert a valuable resource to ancient cultures, Native Americans was the fact they could take chert, like obsidian, with these hard properites and conchoidal fracture property, and they could take this chert and shape into tools....." I never said chert was obsidian or vice versa.
I've learned more about rocks from you than an entire lifetime...
These are the best videos I found on the internet for identifying rocks in hand samples.
You are an outstanding teacher.
I just love your channel! Being a new rockhound starting my rock journey this spring 2024. I have watched almost all of your videos, and I have learned SO much from them. I still rewatch and learn more every time I do. Thank you so much for sharing them.
Many thanks for your kind comments. Glad it's helpful!
Thank-you. Haven't sat in a college classroom in decades so this was a real treat. I love learning new things in the sciences, esp. physics, geophysics-volcanology in particular. This was great! I had never really seen the different grades of coal before, up close-very informative! I especially love your walking lectures. Please keep them coming.
I never realized that coal was so soft. That Anthracite doesn't look soft, but you showed that it is basically charcoal, or Carbon. My son has found Chert arrowheads here in New Mexico along the old trails along the Rio Grande river. Excellent presentation Shawn.
The husband and I started rockhounding on the beaches of all the Great Lakes a few years back and still find identifying our rocks/minerals so confusing. I’m learning so much from your channel! I love it! Thank you Professor! 👍🏼
Hi, I'm in Northern WI and go up to Lake superior. I too found rock identification very confusing. These videos are amazing. So happy I found this channel. Happy rockhounding!
I love chert. When I was a kid, teachers showed us how to work chert. This was before there was anything worth watching on TV, so we put quite a bit of time into learning to work chert and got quite good at it.
No chert, no choose, no Cervus!
Absolutely love that series. 👍
I've come across chert when I've been looking for fossiliferous limestone. I used to think I lived in a geologically boring part of the world, but this series has maybe shifted my outlook. The glaciers deposited so many different rock types, and I was kind of blind to that. Next time I'm oot and aboot, I'm going to have a different eye. Thanks Professor!
@@rodchallis8031 where in Canada are you looking ? I'm in the foothills of alberta , Hinton
@@MatthewRitchieTheNextChapter SW Ontario
This lesson has been especially pleasing as I find both Chert ( Flint ) and Coal truely interesting and quite fascinating how biochemical processes make rock. Nice example of chert in limestone and the Anthracite was a new one to me. So a simple piece of bituminious Coal, even the youngest must still be about 50 Ma !
Great video, I’ve really enjoyed the sedimentary vids, being from the WV-KY area that’s all I ever saw as a kid, I still remember being shocked when a 10 year old me learned that coal isn’t found in about every rock cut like here in East KY-WV. I think that’s when my interest in geology started
Great and timely information! I just returned from a birding tour in So Texas, and brought back samples from Star Base, Boca Chica, Rio Grand, (and at Indian Point there was a whole jetty of limestone)! Thank you! 🥰
You are the best teacher in the world. Im from Brazil, but i always see your videos
Wow, thank you! I appreciate your viewership. All the best.
Soo good, in fact that Socrates , when apprised, drank a cup of Hemlock to him!
Watching what Chert is on this video was definitely better than just reading the text file we got from our teacher, thank you!
We out west haven't really ever seen coal up close. This is my first time. 🤯🤯🤯🤯
When I was born, the house we lived in was heated with coal. And now, 64 years later, the only coal used here is probably by hobbyist blacksmiths. it leaves a mark, though. Last summer, I was investigating an upturned tree along the local river. The dirt pulled up in the tree roots gives a picture of what's under the ground. Sure enough, I found small bits of coal. I'm guessing industry and home owners probably dumped their ash into the river, and these were small unburned bits that got deposited on the river banks during annual spring floods. If coal was ever used where you live, you'll probably find traces. Old houses will have a small "window" in the foundation. That's the old coal chute door. Dig around one, you'll probably find nickel or quarter sized bits of coal.
Very informative presentation. It was great seeing close up example of the rock. I have been surprise to find that we had coal mines not far from Portland. This was also tied in with the gas fields that are still active today. It speaks to a way different eco system then we have now.
Best teaching geology videos on the net! Thank you! I appreciate you, your knowledge and for sharing your years of studying. This is exactly the kind of videos I have been searching for.
Thank you so much for sharing your knowledge❤
I've run into a similar breccia type material here in SW PA/WV--Along the Cheat River. It's definitely a conglomerate found in conjunction with limestone. I think the local Indians quarried it for their lithic material needs. I find it, oftentimes, quite near artifacts as if they sought it out for a specific purpose.
Enjoying your videos! Way more than actually attending a college class. As a 47 year old Iraq veteran I can't deal with the students like I once could. God bless them.
I learned that many of my backyard rocks are cherts. Some have that smooth surface texture, with a brown mustard or chocolate color, and others have rougher, gray, tan, etc surfaces. Some polish up to look like tiger's eye. It's fun to discover what lies beneath the surfaces of common rocks. Also, great shirt! That's a good color for you. Thank you.
Thanks so much for your timing for this video. A real help for my current projects!
You are amassing quite a library, thank you!
Thanks for your outstanding class , please keep update us.
Thank you for making these videosfor our educational purposes!
Thanks!
Thanks for your kind donation in support of my geology videos, Allan.
I'm learning a lot from your video's, especially after visiting many of your topic sites in Idaho.You explain the subjects so well ! Thank you
Glad you like them!
Thanks for sharing so much information in all of your videos. Learning from your videos definitely adds another fascinating layer to my collection of rocks!
I really like that shirt. The colors are great. Thx for the science also
Love your videos! This one is especially interesting to me because I love agates. I’d love to see a video specifically for agates.
You answered one of my long time questions .I have chert in limestone. And it's not a fossil I'll keep on looking
Thank you, Shawn!😀
Very nice video. I love the descriptions that taught me how to tell the difference between the different types. I'm very familiar with getting cut by a piece of obsidian... not fun... was not expected... and I had a sliver of it that I had to dig out of my finger.
Ouch!
so much info that really helped. lots of jasper and coal here in the ohio river basin so this video was exactly what i needed, thanks shawn:)
wasnt sure if a certain piece i had was coal or not, and your technique of putting pressure on it was the key. heard a light cracking sound, then i knew:)
Glad I found your channel, I've always had some interest in rocks! Thanks for the pronunciation of "chalcedony" -- I was pronouncing it to myself as rhyming with "alimony"
Me too. Never heard it pronounced, so we did our best in a guess, right? Haha
NOTHING rhymes pleasantly with alimony. Child support, YES! Contending hate-greed , though DOES rhyme with alimony, in case you are a lyricist, inclined to odious odes..
Here in East Texas some commercial parking lots have treed islands using rounded Arkansas river rock as ground cover. Most of it appears to be chert, marble and other hard stuff that's often banded or a banded conglomerate. I kept one that's red chert covered with small white dots and fine whites that go in all directions and slightly wider white lines that cross each other at right angles. You an play Tic Tac Toe on it! The rocks came off the ancient Ouachita Mountains so there's no telling how old those may be.
I never knew peat was a rock! It is interesting to see the different ways that academics and industry differ. Industrial coal usually starts with Lignite and goes up from there to sub-bituminous, bituminous, and anthracite. In coals value for heat production is the highest is the best grades of bituminous because it has a substantial amount of heat from the hydrocarbon content that is lost as it becomes anthracite. Another distinction is metallurgical grade coal which is bituminous coal with low ash content and low amounts of impurities that are a problem to steel production. This coal is common in western Pennsylvania and is the reason Pittsburgh became a center of steel production. Anthracite was favored for it's low amount of soot when it burned and that made it's primary usage for heating in urban areas. For a long time the British navy had first right to anthracite coal in the UK because it didn't leave tell tale smoke trails behind their ships.
You are an amazing teacher
Professor, what factors cause segregation of silicate organism detritus from calcareous organism detritus? Why aren't silica and lime mixed together in rocks originating from seafloor oozes? I've always wondered what determines where radiolarian chert forms versus where limestone forms.
How they form together but differently.
According to the USGS peat is a precursor to coal and there is lignite (mined here in Texas), subbituminous, bituminous and anthracite. The lignite mine associated with a power plant had piles of petrified wood that came out of the mine.
Yes, I left lignite out because I didn't have a good sample but lignite fits between peat and bituminous coal.
Just watched this video, I am from quebec canada. I found rocks on a riverbed while fishing, I had beleived that they were coal.they are a pretty solide black rock ,dull in colour and you can write with them. my research show me that they were coal. are they possibly something else. I know coal is not usaully found in river beds but there are lots of mountains around.
Great video. Lots of chert in central Texas
Learned a lot from this. I had no idea that chert had biochemical origins.
What happens when the metamorphism of coal goes beyond anthracite?
Thank you!
Good question. I believe as temps and pressures increase, anthracite turns into graphite (the mineral made of pure carbon).
We have chert here Thanks
Great stuff Shawn. Thank you.
There's also an Oregon coastal coal bed - Eocene age. It was used for transport and heating in the latter half of 1800s.See the Coos Bay- Coquille formation.
Great presentation
Hi Dr. Willsey. Totally unrelated question here (can’t find a way to message you about it). In Southern California near the town of Boron, there are some beautifully colored mountains (when they’re mined) that look just like the rhyolite mountains in Landmannalaugar in Iceland. Are they rhyolite or are they something else? Thanks!
I don't know the details but likely hydrothermal alteration of rhyolite and other volcanic rocks.
Thank You!
Very interesting. Thank you for sharing.
First time I went to visit my wife's grandparents in southeast Kansas I was shocked to learn that area had coal mines.
Interesting, I didn't know about coal in KS. My grandfather was from Central Kansas. There are stories in the family about going to the chalk hills. I had also heard about chert being found in KS. This is making the geology of the plains more interesting to me.
Thanks, professor!
Love this rock identification stuff. It's so cool. As you probably know, i'm a new comer to your videos, as well. I wanna see all of them. I hope to have this question answered....At what degree of metamorphism, heat and pressure, does coal become anthracite?
I learn a lot from you
this is quite good session.
Another good one ,thanks.
Great learning again thanks
EXCELLENT!
Great you have samples of flint from Dover UK. It was used widely for houses and churches. I've always wondered why they were deposited in layers, (horizontal bands). Anyone got any thoughts/ ideas why this is?
I'm enjoying rediscovering rocks again. Thanks!
Excellent 👍👍
Great video, Sir! 👍👍👍👍🇺🇲🇺🇲🇺🇲🇺🇲✝️✝️✝️✝️✝️✝️✝️
Glad you enjoyed it!
Do you watch Donny Dust Paleo Tracks? He's a rock knapper. And he's very good at it too. You two are on the same page, somehow.
so why is flint associated with sparks? I looked it up:
"When struck against steel, a flint edge produces sparks. The hard flint edge shaves off a particle of the steel that exposes iron, which reacts with oxygen from the atmosphere and can ignite the proper tinder." So, it seems that in order to chip off a small piece of iron, you need a very sharp edge. that's why the flint is needed.
Do sedimentary and cemetery rock have anything in common?
Now I really know what anthracite is !
Would shungite be considered a type of anthracite coal?
Yes. The highest grade of coal.
Very few people know that coal has pyrites. I worked in a coal burning power plant for 23 years. They use pulverizers to crush the coal into a powder they blow into the boiler. There is a chute at the bottom of each pulverizer for the pyrites to fall out, because they're harder than the coal. I've seen where a lot of gold miners find pyrite and they call it fool's gold. I wouldn't think that gold would be located with coal. Is there a connection or it is coincidence that pyrite is found with gold and coal?
If I'm not mistaken pyrite mainly forms under anoxic conditions. Which tends to be the condition under which plant remains become coal. So there is indeed a connection.
This is interesting to me. When you mentioned that, I realized that all the times I have found pyrite is in Central Washington, in Cle Elum/Rosslyn area and also the nearby Blewett Pass area. In the first area, there were coal mines. In the Blewett Pass area, there were and still to a limited extent gold mining. These areas are actually fairly close to each other. In addition, the rocks removed to get to the coal are layers of red sedimentary rocks that are packed full of plant fossils. Which to me makes complete sense. I am only a lay person learning a bit more geology. My mother was from Illinois. When I was a child, she told me about the types of coal. She was telling me a little about mining as we drove through West Virginia. She had also grown up in a house with a coal furnace. The first coal I saw was waist left in the coal bin room of the basement of that house.
@@Anne5440_ I had heard about coal in WA, but it was my understanding there wasn't that much of it or it was hard to get. I know there is gold around Liberty. I visited that area in Sept. of 2021.
When I was working in a coal powered power plant, we got half of our coal from IL. Of course, in the power business, cost is a big factor in where they buy the coal, plus the sulfur content and hardness, and other factors are considered. But that wasn't my department. I just burned it to boil water. 😀
@@7inrain I can see that, as we got tons of pyrites from coal in a shift in the powerhouse. But why is it around gold? Seems like two very different sources.
@@GregInEastTennessee _"But why is it around gold?"_
I have no clue why that is. Guess that has to be answered by Professor Willsey.
Funnily enough I have one piece of limestone consisting of fossilized corals on my bookshelf. And it both has tiny crystals of pyrite and a few microscopically small flakes of gold on it. So what you experienced I did as well.
❤
Excellent🎉❤🎉❤🎉❤🎉❤🎉
What about jet?
Lignite is the lowest rank of coal. Correct?
Technically peat is. So, peat, lignite, bituminous coal, anthracite (from low to high grade).
Is that chert and coal or chalk and cheese?
👍
Had to check it twice: you basically stated that obsidian is a chert. I do not believe that obsidian is classified as a sedimentary rock. Rather obsidian is an igneous rock produced from lava flow which contains lighter elements such as Si, O, Al, Al, Na and K. Also , obsidian has a shiny glassy sheen, unlike the Cherts which have a softer duller sheen. Just saying.
I did not state this. I know the difference between chert and obsidian in terms of classification. Also, note that I have a video on Igneous Rocks featuring obsidian: th-cam.com/video/xX6YGpk3DWk/w-d-xo.html
In the video you mention (with chert), when discussing conchoidal fracture, I state (at 2:07 mark): "this is what made chert a valuable resource to ancient cultures, Native Americans was the fact they could take chert, like obsidian, with these hard properites and conchoidal fracture property, and they could take this chert and shape into tools....."
I never said chert was obsidian or vice versa.
i want ur autograph
the lowly life of the fern....
hooray for metamorphosis.... and... moses... run....
cryptocrystalline... hard to unravel... plate tectonics... conchoidal factures....
Thank you!