Learn Rock Identification with Two Geologists

hey there I got a special treat for you today we have Paul and Nat here we're a couple of geologists or a geologist couple I don't know how you say that but either works so they're going to be identifying rocks for us today and uh you guys both have phds right so you're highly qualified that's that's a rumor okay and I just know a pretty Rock when I see one and Nancy taught a middle school earth science for quite a few years so I'm not prepared to identify anything she's she's more qualified than I am uh so now we're just gonna pick up rocks and uh people are going to tell you what they are and it's probably not going to be me I forgot to mention this is Lake Superior we're in the Eastern U.P and Nat already has her hands full so what do we have here this is porphyritic rhyolite rhyolite is a volcano Camp Rock and porphyritic refers to the fact that there are two different sizes of crystals in here you have these bigger white feldspar crystals and then you have the smaller reddish what we call Ground mass and so this would have erupted out of a volcano long long ago did you have others I thought you had several already I also have a nice uh nices are mcrox form under high heat and pressure and they get these alternating lighter and darker layers of minerals in them and uh here this rock probably came from somewhere in Canada and was there a third one or not no oh okay I thought there were three he has one oh well let's go talk to DePaul I have that I have no clue what that is wow I'm not the only one who says that that's not my big that's not that's my big find of the day in the first oh two minutes let me get it wet and take a look um honestly it looks like some kind of weird conglomerate because I see what looks like a clasp there and another clasp here and the Matrix that's holding them together is weathering out faster and so it gets this kind of weird shape okay so what do we have there so here we have two intrusive igneous rocks these are formed from magma that cooled and solidified underground so we get some bigger crystals in them but you can see these have different colors to them this has a lot more pink in it this is all black and white this pink is potassium feldspar and when you have one of these intrusive igneous rocks with lots of the potassium feldspar we call it granite this one is more black and white it has more flagioclase feldspar and none of that potassium Felts far and this is called a diorite so it's a little different composition it also has less Quartz in it than this one so these interests of igneous rocks have some very um there's a lot of different names for them based on the exact mineral composition and if we don't know the exact mineral composition but it has this texture this size of crystals we call it a granatoid so I'm safe if I call them all granitoids you're safe to do that good good to know what'd you find Nance I found a small banded shirt doesn't have the dark bands that we kind of typically look for but it does have some nice banding in it that's a pretty one this is a unicite which is a pink potassium feldspar and um epidote and this forms because after a rock formed you have fluids going through it which Alters it in something called epididization and replaces other minerals and uh emplaces the epidote to give us this beautiful pink and green rock that's one of my favorites to pick up polishes up really nicely well Nancy just handed this one to Paul and this is what I call a maggot because it looks like it may be an agate but let's get a professional's opinion what do you think Paul well the mag it's just that's a that's an awful term for these things um I would actually call this um chalcedony it's bordering on an agate not a Lake Superior Agatha because remember Lake Superior agates have to have that kind of that reddish whitish coloration so this I would call kind of like maybe a chalcedony it does have bands in it though and chalcedony is just an umbrella term for things like church Jasper Agate um Onyx things like that it all fits under that chalcedony umbrella and then there's all the different Rocks Under it depending on color and stripiness and things like that [Applause] so here we have another igneous rock and this one you can see some big crystals of feldspar in there I'm not seeing a lot of quartz in there so this would not be considered a granite this is one of those other igneous rocks and maybe a monzonite but I haven't looked closely enough to get the exact chemistry and the exact mineral composition of it and that's just the thing to remember about these these granatoids is there's a lot of detail you have to look at if you want to identify them perfectly I have three different rocks here now these two are quartzite and quartzite is a metamorphic Sandstone if you look at them very very closely uh especially using a little magnifying glass you'll actually see the little quartz grains that made up that ancient Sandstone that got metamorphose and they can have different colors and appearances simply because they just had different parent sandstones now over here this is a different rock this has a quartz vein cutting through it and so what happened we had this igneous rock here which is probably a type of Basalt and later on hot Waters flowed through that and left this quartz behind and that's quartz the mineral that precipitated out of the water so I think you guys have already discussed corporate perforated rhyolite this is poor Frederick Basalt so obviously similar process the light Crystal greens that are larger the quartzy things would have pulled first and slower and gotten big and then the Matrix would have cool faster and has smaller rings so this is a brecha and brechas are made of little bits and pieces that have very angular edges and you'll take a look at those little bits and pieces in there angular edges on there and uh this brecha it looks like that might be a little bit of Jasper that got broken up and incorporated into this sedimentary rock but it's a horn coral isn't it a horn coral this is something that you don't find on Lake Superior very often because Lake Superior is full of igneous rocks and some metamorphic rocks so you don't see fossils along Lake Superior so that what this tells me is that this came all the way from James Bay and Hudson Bay there would be uh there's beds of limestone and carbonates in that area and any fossils you find along Lake Superior is going to come from there come from James Bay Hudson Bay and got transported here by the glacier long ways from home ways from home so what we have here is a felsic igneous rock cut by a mafic igneous rock so this Dyke cut through the felsic igneous rock now what you might notice is that this is weathering away the darker mafic stuff is weathering away faster than the felsic material there's actually a little indentation there that's because mafic minerals that's going to be Olivine and pyroxine and some of the uh certain types of feldspars weather away a lot faster than the felsic minerals of quartz and potassium fell as far and so and so we have a little bit of differential weathering here where these are holding up against the battering the Lakes giving it better than this area so this is a unique quartzite because we have quartzite and then we have some of these dark layers in there as well and just like at a beach today or in a river today you get sometimes these layers of black sand in there same thing happened long long ago and so we had you know our quartz sand and then some of those heavy mineral layers it all got metamorphosed into this quartzite showing those different layers so this is also quartz um but this is the mineral quartz not the metamorphic rock quartzite and when I looked at this using a magnifying glass I couldn't see any of those little quartz sand grains of an ancient sandstone and so how this would have formed we would have had a vein of quartz just the mineral being deposited and that weathered out and has been tumbled along the lake creating this nice round Cobble here so the mineral quartz versus the metamorphic rock quartzite so is it safe to say if I find a layer of quartz or a vein of quartz it's always quartz and never quartzite yes okay good to know so we've so what we got here is something actually pretty rare along the Lake Superior Beach so we have the rock here probably some sort of a basaltish looking thing but in these areas here you see some purple and if I rotate it around here get it just right in the lace that's this one up here I don't know if you're gonna be able to steal the camera or not sometimes you get a little bit of a gold glint to it and so what this reminds me of is a feldspar and not a great quality labradorite but nonetheless a labradorite um and again if that's just get it in the right light here I can't quite get it right let's see it was a lot better A little better thing see if we can get it here a little wet here myself but if you look in there if I kind of roll it around a little bit you might see a gold glint come out of that purple and what that has to do with is the way the feldspar grows where you get these twin planes uh the crystals mirror each other and so what happens is when the light goes in it kind of bounces around in there a bit and as you roll it around you're seeing that that effect that what we call Schiller effect so a lot of times in the water here you'll see kind of a line of black kind of through here is black and then over here there are lighter colors so does that happen do they get stored in the water kind of like gold panning by density yeah eventually because of the water will drop off heavier denser things in certain areas so yeah it's just like gold panning so what are the black rocks you got a couple there well well frogs aren't all the same thing uh in fact here we have an igrock which rudimentary BlackRock this is from the omara luck formation and this is a gray wacky which geologists sometimes call a dirty Sandstone if you look really closely you should see some little sand grains they're a little bit lighter colored and that's going to be some quartz and some feldspar and why we call it a dirty Sandstone it also has a lot of clay and silt very fine-grained material in there and and that surrounds that quartz and feldspar and this Omar a lot comes all the way from Hudson Bay the basalt is much closer that's from here in Michigan and so two black rocks but very different histories so this is uh gray wacky but at marlux I usually think of as with the holes in them but that's from the same formation but doesn't have the hole right and so same formation that uh the or marluck formation but in some areas the omara look formation had these things called concretions in there it's where there's some preferential cement and it was made out of calcite or carbonate material it preferentially weathered out leaving this hole this nice round hole behind so not all black rocks are the same on a beach all right so just to follow up what Matt was saying earlier about a marlux so this is one um this is again a gray lucky so a dirty Sandstone I have a fly biting me and so these come all the way from Hudson Bay in a place called the belsher islands or Belcher Islands I've heard it's called both ways there's a little Peninsula that sticks out where these are located this formation it's called the immoral look formation this is about 1.7 1.8 billion years old rock and it's thought that these are a result of what's called a turbidite deposit which is basically you can think of it as an underwater Landslide or an underwater debris flow and so what happened is under water this landsliders the breeze flow Stir It Up the water and posited deposited the layers of sealed and sandstones and such down and then over time these got very slightly metamorphosed into this dirty Sandstone is gray walking these are used to track glaciers because obviously we're nowhere near the Belcher Islands up in Hudson Bay so what they do is they use these omara locks so he's on Mars to track the movement of glaciers as they've come from Canada down through the Great Lakes so you find these all over along the shores here of Lake Superior you can also find them out in other places such as Manitoba and Western Ontario as well and I've even heard them being bounced her down into the into the Dakotas and it really makes it nice to understand the movement of glaciers to pick these up all the way from Hudson Bay and transport them down here so here we have an igneous rock that you'll see these silvery spots in there and that's the mineral muscovite that's a type of mica mica's peel apart really easily they break it down really easily which is why you don't usually find those on the beach here uh because the lake has tumbled these rocks around so much usually those have broken out muscovite is actually quite common in a lot of granites and a lot of metamorphic rocks but like I said breaks down really easily so you don't usually see it on the beach like this and it breaks down in tumblers also which gives little pitted effect and I don't like that so that's why the granite stay stay behind on the beach so this rock here uh I would call a brecha because we can see these pieces inside there now this one's a little rounded but the rest of the pieces are very angular and when you have a rock made of angular pieces inside you call it a brecha all right the Flies are coming out so Nancy is donning Her Fly pants these things are Lifesavers though when uh when the Flies get bad and they're just coming out because it's getting warm out okay and they hit your legs mostly so we have fly jackets also but the uh the pants are the part you really need all right when that says ooh we know it's a good one well this one's really neat because we have a metamorphic rock here uh but we also have a few little faults right there you see how this layer goes here and then it's offset right there so after this rock formed it got broken and these pieces shifted in there so this is neat it's a rock that captures uh some tiny little salts is that a nice before it yeah it is that was a nice it still is it's just a nice with nice little faults so what we have here this this very uh distinctive kind of sorry about the fly this very distinctive uh yellowish color right there and uh that's Limonite and Limonite is an iron mineral and you'll often find it staining the outside of rocks so this is a pretty unique Rock here what we're looking at here is a granite but you see those black spots in there what you're looking at is the ends of Tourmaline crystals this is what we would call a shorel the black tourmaline and how we know that it's shorel you can see some of these end pieces here you can see they're kind of almost rounded triangles because the best way to describe is when you look at these crystals on end and these these little shorels are scattered all through this rock especially on this side here and so it's quite a unique rock you don't see these every day so is it a long narrow Crystal they are they tend to form long narrow prisms okay so if we could look inside this rock you'd probably see the these long crystals like you can see right here that's what I was looking at right there these other ones here probably look the same way if you could look inside that rock so I just found a little agate and a minute ago you said that Lake Superior a gets are red or tend to be red the classic Lake Superior Agate is that nice brick red with white banding in it coloration but there are other colors of Lake Superior AG I didn't mean earlier to say that only the red ones relates for your agates because I have some that kind of have a purplish gray color to them that were found on Lake Superior so while yes they are Lake Superior agates they're not that classic brick red and white coloration banding so I've noticed from my limited experience in the Western U.P or Minnesota they tend to be more that red color or orangish color yes and here it seems like we find more variety is that my imagination or is that a real thing imagination that is a real thing um you tend to find more of the reddish the reddish colored ones in Western Lake Superior and then down through Minnesota into Wisconsin and all the way down they found them as far yourself as Iowa and Kansas they have found lakes and that's that's iron staining right iron staining and that's where all the iron mines are coincidence I know okay kind of um agates form and basalt basalts have some iron in them oh okay and so that's where they're getting their red color from is the iron that that iron in the basalts themselves oh okay I didn't realize that good learning stuff here learning stuff today um so what we have here is a structure that's sometimes found in metamorphic rocks called budinaj and that's where you have this thin layer it gets a lot fatter and then it gets a lot thinner and then it gets a lot fatter again and that's actually named Boudin is a type of sausage and people saw this like fatter thinner fatter thinner and they thought it looked like links of sausage and that's how that gets its name that's hilarious all right so I've been wondering what this rock I call mystery rock is for years and so Matt just broke one open so this is unbroken and when I broke it open it breaks with this classic concoidal fracture and these sharp edges of micro crystalline quartz really really tiny crystals of quartz which we call chalcedony and that's why it has also it's a bit translucent uh has this really pretty color and when it's when you see it on the beach it's bounced around and so it gets a little frosted you break it open you get those nice colors there I can't really tell you how it Formed because this sort of thing can form in a lot of different environments so just a beautiful mystery rock that's actually chalcedony so here's a couple other examples that we get now this one has looks like Jasper in it which is a chalcedony right it's a type yes and then there's more of that that what you have on top then there's another one so they're still uh they're chalcedony but still a bit of a mystery how they formed or where they formed or there's there's a beach like this it's hard to say because the Rocks come from all over it's difficult to tell exactly where these came from all right well thanks so what we got here is a rock that is found here but it's a little bit rarer than what you might expect we're at the kind of central the eastern part of the U.P Upper Peninsula and we're finding jacobsville Sandstone here and you might think well wait a minute isn't jacobsville restricted to the Kiwana Peninsula no it's not it is found over this way but it gets thinner and thinner and thinner the more East you move along Lake Superior and so you find these occasionally you find these little these nods where these rocks here um this one here has had some reduction done to it you can tell by the red or the white here the white is actually the reduced part where you've had some sort of um some sort of organism some sort of bacteria or whatever um there's photos called organisms right now that basically loves the iron in these rocks and so it'll actually eat this iron here and leave the more wider parts so we have an igneous rock here and then when I look at the other side there's this dark colored metamorphic rock and what this looks like is this is a Xeno lift which Xeno means foreign lith means Rock so it's a foreign Rock and what happens when you have igneous intrusions you have this magma Rising upwards towards the surface it sometimes picks up and uh kind of engulfs some of the surrounding Rock and that rock doesn't melt it just gets stuck in the magma and so it's this foreign rock this xenolith in the magma so this is a rock it's a rhyolite that has these beautiful blue crystals in it and if you go down to Texas there's a rhyolite with beautiful blue crystals that's called Lanai this is not lanite and I can tell you how it's different lanite is indeed a rhyolite with blue crystals of quartz blue quartz is very very rare this is a rhyolite and the bluish crystals in this are feldspar so even though it looks similar they are different minerals so they are a different rock type so we have this really neat Rock here it is very magnetic and you'll notice these little pieces in there that are all surrounded by red and so I know this is magnetite because it is magnetic it's nice and heavy like this but I'm not sure exactly how it Formed um you know these could have been magnetite crystals they could be rip up clasps where bits of banded iron formation got picked up and the edges got oxidized um I honestly don't know exactly and that's okay in science to say I don't know the answer right off the hand so what I can tell you it's really neat magnetite so this is a Basalt that um was the top of a lava flow and at the top of the lava flow you have the gases in the lava bubbling out and towards the top there's less pressure on it so the bubbles get bigger and that's why you see these small ones down here and bigger ones towards the top now the thing about it is the vesicles a little um uh gas bubbles are filled in so they're properly called amygdals and in this case they're filled in with quartz so right here in this rock we have this little reddish stripe going through there and if you look really closely at it you can see it follows a crack in the Rock and this tells me that hot water was flowing along there and it caused a little bit of hydrothermal alteration so the hot water had some minerals carried in it and it also just was hot and so it altered the rock as the water flowed through there there's all different kinds of hydrothermal alteration that can happen to rocks and it can really change their appearance and so it's kind of neat to see this little localized area where you know it was changed by that hot water so this cross bedding in the jacobsville sandstone and cross bedding is where you have these layers that are at an angle to the other layers and this forms when you have a current either wind or water pushing sand and it pushes it into like little Ripples and you get these cross beds forming in there and in this case it was water it's basically a river flowing along that was creating these cross beds as it was flowing so it looks like we have a visitor from a foreign land here on the Eastern U.P this this looks like something you might find on the human eye pencil over you have the salt you have some quartz here and then around it you have some epidote surrounding that quartz and so this looks like a lot of the material you'd find up in the mines up in the quinoa so why it's here I don't know maybe maybe Lakeshore drift started here maybe uh post hominid Glacier post glacial hominid activity um either way but it's something that's something that's unique here we haven't found anything like this today until now yeah I was afraid you're gonna say it was from East Lansing well in that case that's what I say well I heard everybody talking about amethyst down here so I thought well why not go show a piece that I found myself just at the same time I came across some purple that's neat yeah don't do too much of that around here it is around Rob just handed me this rock and uh correctly identified it as a quartzite but this court site did not start out Life as a pure quartz Sandstone that got metamorphosed it actually was like a dirty Sandstone that had some silt and clay and mud in it and the Silton clay and muddy stuff ends up getting changed into garnets when this Sandstone got metamorphosed so we have a quartzite with some little bitty garnets in there that were formed in metamorphism I I didn't know it was so cool I just thought it was stripy [Laughter] and this little guy I think it's probably just the middle of an agate and a doll on top even when wet but it's still a little Leggett so right here this is a sedimentary rock that looks like it might have been metamorphose just a little bit because this really looks a lot like a mudstone but mud stones are very weak and they break apart really really easily and I wouldn't expect to see it so nicely rounded and holding up this much so this is either being baked a little little metamorphose or it might also have been solicified a little bit just to make it more robust and hold up against the pounding that the lake has given it so started out as a mudstone and got a little bit stronger and is being shaped by the lake I just found a egg it not the best one ever but it's definitely got some banding around that quartz pocket there you found the big prize huh an agate it's not the prettiest Agate in the world but it's an agate so I'm happy yep let's say you definitely see the bands on that so this very sparkly rock that you see here this is a schist which is another type of metamorphic rock and schists have a lot of mica's in them mica's are things like muscovite and biotite they're very flat minerals and so they form these kind of sparkly layers in schists now this is a schist there's lots and lots of different types of shifts that can have lots and lots of different types of minerals in them so they won't all look like this one what we have here is a banded iron formation so you should be able to see those nice little layers in there that's the banding and then you might even see some sparkles uh metallic Sparkles that's either hematite or magnetite so banded iron formation and these are very interesting rocks that formed in the Precambrian then they formed because we had a big change happen on Earth at that time there's What's called the Great oxidation event that occurred about 2.5 or 2.2 to 1.8 billion years ago and what happened in the great oxidation event is the atmosphere of Earth changed from having no oxygen in it to having oxygen in it and that happened because photosynthesis developed and photosynthesis pumped out oxygen into the atmosphere when there's oxygen in in the atmosphere iron can no longer dissolve in water because it will bond with the oxygen and become insoluble and precipitate out and so during that great oxidation event these banded iron formations were being created all right so we made it back off the beach and uh Paul has has been busy he wrote a book huh I wrote a book I've been very busy the past few years so tell us about it I I've seen it but so this book it's called Michigan rocks it's through Mountain Press publishing it's the same group that does the Roadside Geology of whatever state you're in and it's a book it's 56 stops within the state of Michigan that any person can go to with the book and basically looking in this book will tell them what they're looking at the geologic history it has great maps in it great figures um I think it's a great book myself I I read it and I like it too and I especially like the title excellent title very creative our lawyers worked everything else behind the scenes so uh well can we see a couple Pages sure so we'll uh I mean here's there's kind of what some of the examples are Presque Isle Park up in uh Marquette um I'll find another I guess Mackinac Island is featured in here um it's listed by section fossil Ledges this one I especially like because I included a geologist for scale oh and I thought was very uh very appropriate for the day yes but again it's just it's all throughout the state um basically from The Keeping Up insula down and across the up and then not quite as much in lower Michigan because well there's all that glacial cover that's covering it up so um but again fantastic book um I obviously highly recommend it I do too uh you'll definitely learn some geology if you read this book good stuff so we'll put a link to that at the end of the video and uh we'll see you next time oh there'll also be a link here to our video last summer uh if you missed that one you got to see that because we did the same thing as this one only on Lake Huron instead of Lake Superior talk to you later

Channel: Michigan Rocks

Views: 102,200

Keywords: Michigan Rocks, Paul brandes, nat brandes, geologist, rock identification, Lake Superior

Id: lWTgUbdccJE

Length: 33min 24sec (2004 seconds)

Published: Fri Aug 11 2023