Learn to Identify Lake Huron Rocks with Two Geologists

hey everyone i'm here with paul and nat who are both geologists so today's video is going to be about identifying rocks on the beach and they know a heck of a lot more than i do so they're going to be doing most of the talking all right what do you have all right so right here this is a sandstone a very fine-grained sandstone but you'll notice there's two different colors there's this reddish area and this pale area and that has to do with reduction and oxidation zones there's a little bit of iron cementing the sandstone together and when it's oxidized it gets a reddish color when it's reduced it gets this whitish sure tan color and that's controlled by groundwater flowing through the rock and that either oxidizes or reduces that iron so we have this nice colorful rock right here we have granite here and we have granite on the other side and what that suggests to me is that this is the original rock and then this squeezed its way into that and came later and so we have some quartz and other minerals that were precipitated later after the granite form all right so what we have here this is like an algal mound or a cyanobacteria mound where these organisms are growing upwards capturing some sediment but this is not a stromatolite because technically to be a spermatolite it needs to have a dome shape to it which this does not have so here's one i can identify myself with no problem that is shirt banded shirt and those always go home with me because they look great tumbled so this is a limestone that has intraclasts in it and what happened with that we had limestone being deposited then we had a storm come up and the big storm waves ripped up bits and pieces of the limestone that had already formed and then created this rock from those bits and pieces so the intra means the pieces come from the previously deposited limestone and there's fossils in there right there are fossils that got ripped up as well there's like a little piece of coral right there and right there and right there all right so what we're looking at here is called a porphyritic granite and what you see here is this granitic ground mass here but you see these large potassium feldspar crystals within that grant that tells me that this has two different stages of cooling where the ground mass cooled quickly um finer grain but these coarser green feldspars pulled slower slowly in this rock so obviously not from here obviously from canada but a very neat rock very nice uh very nice portfolio granite all right so i have a lot of viewers that ask me about like the bluish rocks the greenish rocks on the beach they're kind of plain i don't pick them up because to me they're not interesting for lapidary purposes um so can you tell us what some of these things might be all right so these all look very similar but they are lightly um very different rocks what you have to do is look at them um in detail with a hand lens or a magnifying glass and if you look at this one you'll see little flakes of mica in there and this is probably a mudstone a micaceous mudstone or maybe uh it's been metamorphosed a little bit into like a um a horn fells this one if we look closely at it it is uh very dark very fine grain that's probably a basalt this one i if we look at it wet you'll see if you look closely lots of little white and black minerals that are interlocking together this is an igneous rock and this is quite fine grain but i'd still put it at you know maybe gabro to diorite type rock and more on the mafix side and then this one i'm gonna get a wet you can see it a little better that way and this is a metamorphosed basalt something that we call a green stone and so even though all of these tend to look very similar you have to look really closely at them and at the little minerals that make them up and that will help you tell what kind of rock they are okay now you just said something that's going to cause questions you just call that a green stone you don't mean an isle royal green stone right greenstone's one of those words in geology that has a number of different meanings greenstone can be a metamorphosed basalt greenstone can be the mineral the isle royal greenstone and greenstone can also refer to a type of metamorphism like certain metamorphic conditions and that's just one of those uh words you have to know in geology by context what someone's talking about so what we got here is a very nice piece of red jasper um for this beach obviously again not from this area probably most likely from canada brought down by the glaciers but really a nice red color on there so this is a red rock red rock that's not jasper though it's not jasper that looks like some sort of a metamorphosed um kind of a sandstone looking rock here you can just tell just by the color and also by the grain size if you looked at these two under a hand lens this would be a little bit coarser than this because this is more of a um what we call crypto crystalline or micro crystalline quartz some very extremely fine grain you wouldn't even really even see the grains in this with this rock here under a loop or a hand lens or a magnifying glass you would see the individual grains in there so that's the big difference and the way i tell is because this has concoital fracturing that those little shell shapes almost exactly that would have you broke that air rock into pieces it would just shatter okay all right when we find a really easy one i get to identify it uh that's unichite which is feldspar and epidote the green is epidote and the orange is feldspar so what we're looking at here is a quartzite which is metamorphosed sandstone and just like if you walk along a beach or go to a stream today you'll see places where black sand will get deposited because it's a little bit heavier it forms these like little layers of black sand well that's what we have here this is our quartz sand and then we have these layers of black sand so this tells me this was deposited probably in a stream billions of years ago before it was metamorphosed into this quartzite all right this one i know but i'm going to let paul tell you so even though rob is identifying the easy ones he figured he'd let me have this one so this is a classic pudding stone from the lorraine formation up in ontario near bruce mines ontario beautiful piece beautiful red jaspers um you even got a few different colors here you got some of the more blackish colors a little bit more the pinkish colors here set in this quartzite uh matrix so just a beautiful beautiful pudding song yep that's a keeper for sure all right what do we have here this is a really neat metamorphic sandstone i'm not going to call it a quartzite because look at all of these kind of orangey pinky minerals in there that is feldspar and when you have a sandstone that has a lot of feldspar in it we call it an archos so when we have a metamorphic sandstone with all that feldspar we're going to call it a meta archos now why we have arcos in this is because this sandstone originally when it was deposited didn't get carried a long way from its source area because feldspar as sand gets transported in a river or along a beach will weather away and break down since this rock still has a lot of it in there we know this didn't get transported that far so it tells me a little bit about the history of this this broke down the sediment was transported a little ways then it was deposited as an archos and then it got metamorphosed into this beautiful meta archos all right so uh what we have here this really neat dark rock if you look very closely at it you'll see some sparkly things in there and those shiny gold things are pyrite pyrite sometimes forms in shales black shales and mudstones so what we had here this was originally of a sedimentary rock a black shale or a mudstone with a little bit of pyrite in it it underwent low-grade metamorphism and at some point in the history of this rock we also had these form these are little veins that today are epidote epidote classically has this beautiful apple green color to it flip that one over for a minute yeah this was that's really cool so this rock's been through a lot what you got there this is a stromatochoroid this is a type of sponge and this sponge was a reef building sponge so these would have been all over the sea floor growing upwards in these beautiful layers there forming these like sponge reefs in the long ago geologic past let's look at the bottom of that again and the characteristic of them are these concentric layers uh around where it was growing and then growing upwards now how is that different than a stomata light this is different from a stromatal light because this is a sponge this belongs to a group called the poraferens a stromatolite is created by a single-celled organism called cyanobacteria and these are younger than stromatolites stromatolites evolved much earlier than these did and stromatolites though are successful and do still live today these guys do not this is a rugos coral uh also called a horn coral these were solitary corals that lived in the paleozoic they would this part of it this little point would be growing off the floor and it would be growing upwards from the sea floor with your little coral organism living in the center there hey here's a very common rock what's that that is granite this is rob's favorite rock it is not just a lot of this down here um again from canada brought down by the glaciers um and different varieties of granite too we saw earlier that uh that portfolio grant this one here is just your more typical run-of-the-mill granite a lot of that around here a lot of that all right so this is speckly like the granite paul just showed us so is that granite this is not granite in order to be considered granite it has to have a very specific mineral composition a certain amount of quartz and feldspars in it this one does not have quartz in it the light color you're seeing is potassium feldspar the dark color you're seeing in there are amphibole minerals and when you have that mineral composition it becomes a diurite all right what do we have there so this is another diorite but you'll notice that it looks very very different in this case it's porphyritic porphyritic means we have bigger crystals surrounded by smaller crystals but it gets even more interesting than that sometimes the bigger crystals that have formed will react with the surrounding magma that's still left over and create what's called our reaction rim and this isn't the best developed one but if you look at the edge of the crystal you can see it looks a little bit different than the middle of the crystal and that's where this this crystal has reacted with the melt the magma that was left over as this rock was forming when these reaction rims get very very well developed in these igneous rocks we call that a rapid tv texture all right i know what that is this is nice this is a high grade metamorphic rock the way you identify nice is it will have layers in it called foliation and the foliation will show lighter and darker layers and that's how you identify a nice now a nice the parent rock the thing that this was before it got metamorphosed it could be a granite or it could even be something like a mudstone that just the heat and the pressure altered the minerals and changed it into a rock looking like this nice very okay what do you have so we're going to look at the difference between quartz and quartz site quartz is the mineral and if you look at this you won't see any like little grains or little pieces this is quartzite which is metamorphic sandstone and if you look real close at this rock you'll see what used to be the little sand grains all basically really mashed together so when you look closely you'll see little goths of sand grains in there that you won't see in the quartz so quartz is the mineral quartz site is the rock made from a bunch of pieces of that mineral and then yeah what i've got here is something it's extremely special you have basically quartz cobbles so these were originally quartz that were worn down and boarded by mostly by water probably in a river and then they got incorporated into this four site here so again this is kind of a pudding stone to say but this one's unique in that you've got quartz pebbles of course cobbles in four sides so porch and here's the metamorphic sandstone to quartzite here's a neat rock it's uh some kind of a [Music] breccia conglomerate you can see all the different pieces that make up this rock neat color we have igneous rocks that uh are part of the the clasts within there and just an awesome uh rocket scene like something up rock yeah those would be uh phenocrysts within an igneous rock there that's then within this um conglomerate for maybe goganda till light but we're not 100 sure yeah the color is different but some of the pieces look like they could be really is pretty well what's that one paul that's a very familiar stone here it looks like a petoskey stone also known as a uh hexagon area yeah there we go you get that's a tongue twister that's a really nice one there yep state stone of michigan yeah that's that's a great one yeah it is up nice yeah so what we have here is a quartzite which is a metamorphic sandstone and in this one what you can see are cross beds now cross beds are small layers within a larger layer that are at an angle what those show us is that there was a current flowing here at one point in time when when this was being deposited so there is a little river and that river deposited the sand in these these cross beds and then later on this got lithified or turned into a solid rock and then it even got metamorphosed into this quartzite and so what we're seeing here are these ancient ripple marks probably a few billion years old from a long long ago river all right this is a a piece of diabase it's a very dark rock but if you move it around you'll see some little sparkles of crystals in there this has kind of the same composition as basalt except it's going to have some larger crystals that you'll be able to see in there and you'll probably see those sparkling there so an igneous rock again sometimes you'll find rocks that have these areas sticking out like these layers and what we call this this is differential weathering so as this rock is weathering away some areas weather faster than others and that's usually because this part is cemented together better or maybe with a different mineral that is more resistant to weathering and erosion so this can stick around a whole lot longer than this part and as a person who tumbles rocks i look at that and go no that's not going to work well in the tumbler because we call it undercutting and tumbling where one wears away faster than the other what's that one this is another volcanic rock a very different volcanic rock this is called a rhyolite and in fact it's a porphyritic rhyolite porphyritic means it has bigger crystals in it and you'll see these bigger crystals surrounded by the smaller ones this kind of rock is the sort that would be erupted from volcanoes like for example yellowstone uh when it erupted erupted rhyolite uh this obviously is not from yellowstone but it is a similar rock type so a nice porphyritic rhyolite an ancient volcanic rock so we have a really neat rock here where we have two very obvious different rocks this rock is nice notice the foliation that means the layers and they're light and dark and this is some kind of granite or granotoid which is an igneous rock and i can tell you that this is older than that because this is created by high temperature and high pressure and if you had those high temperatures and pressures this also would have been turned to a nice so either this formed first and then the granite squeezed its way into it intruded the knight or this was something that we call a xeno lift it was an inclusion where the granite squeezed its way into the nice and picked up a piece of it and because this is broken and we just have a cobble like this i can't tell you which one it is but nice which is older than our granotoid what do you have there this is some shirt some this one happens to be kind of a bluish gray color shirt is micro crystalline quartz it's made out of just absolute tiny tiny crystals of ports that you can't see them unless you look at them under a high-powered microscope um this micro crystalline quartz makes up all kinds of neat rocks not just shirt like this but also jasper and agate uh because it comes in all kinds of different colors that forms and limestone right yeah chert is really common in limestone as uh small layers are also what are called nodules one of the places where shirt can come from is from sponges see sponges have what are called spicules in them to give their little bodies a little bit of support they don't have a skeleton and when the sponge dies these silica this these quartz spicules can re-crystallize into little pods of church and that's why limestones often have a lot of chert in them and uh chert was uh used by native americans because you can shape it they would often find these chert nodules and use them to make tools out of arrowheads and stuff that's called napping yeah that's uh napping flint napping flint's another name for uh this micro crystalline quartz and uh so they'd make arrowheads spear points scrapers things like that so one of my favorite rocks along uh these shores this is a gauganda taillight basically it's a conglomerate but these formed during an early ice age on earth about 2.2 2.3 billion years ago this is one of the only areas around where you can find these because again these come from canada and so you find these all along the beaches here but really a great example of one this is a really nice one yeah that's a gorgeous one sometimes the rocks are kind of all the same color in it the little inclusions or whatever you want to call them but this one's got a lot of material on it a lot of variety so nice paul just pointed this one out that's about as good as they get i wish it was a little bit bigger but wow beautiful petoskey stone all right what do you have here all right here's a neat rock this is a limestone and what's neat about this limestone is this dark jagged layer in there that's called a stylolite and that of light uh now it's been a while since i've studied these but as i recall they're formed when this is this is under pressure and you get a little bit of solution and you get some of the impurities in the limestone focused along that style of light that boundary there and uh so anyway a style of light in limestone a really neat thing so this one's called cladopora at least commonly i'm not sure if that's actually scientifically correct but it's a fossil and a dark matrix and uh matrix smells like oil when you cut this one what you got there paul what we got here is a porphyritic basalt and you can tell it's porphyritic by these little kind of greenish white little bubs in there those are little crystals um not sure exactly what those crystals are but um obviously something a little different this however is nothing like amygdaloidal basalt because if you look at some of these grains here see how they're kind of they kind of grow into the rock here a bit so where an amygdaloid basalt would be a very sharp contact and they'd also be more rounded than this so again another product of the glaciers from canada um let's flip it over here you can see some more here but yeah definitely an interesting rock um along this beach so amygdaloidal means there are there are bubbles in there gas bubbles colloidal means there are gas bubbles and again they'd be more maybe more rounded i'm sure in some of your other videos you're showing omega little basalt with those round bubbles and they're filled with minerals so this is corporatic again because they're not really round and again these little spots here almost act like they grow into the rock here as opposed to amygdaloids which are more of a sharp contact where the minerals basically form inside um those gas bubbles so natalie has some of her own videos and i'm going to link some here while you tell them about what they'll see there uh they'll be short videos two to four minutes long telling you a little bit something about geology around the united states

Channel: Michigan Rocks

Views: 239,932

Keywords: Michigan Rocks, geology, Lake Huron, rock identification

Id: F_t4LC13utM

Length: 24min 7sec (1447 seconds)

Published: Fri Aug 05 2022