hello scholars doctor a bear here coming with another video this time on rocks and minerals the core concept behind this screencast is that the earth is a dynamic planet and there are a lot of changes that happen both among biological organisms but also geologically speaking so we're gonna talk today about geology and a little bit and we'll save geophysics for the next lesson next chapter we have here a metamorphic rock we're gonna learn about the ribbon-like layers and the folding and the that occurs there and take a look at the rock cycle this in this lesson the Earth's crust 98.6 of it it was just made up of eight elements so about the majority gonna be silica is going to be silicon and oxygen those are the big major players when it comes to crustal material and then when we start getting into the interior of the earth we're gonna see iron is going to take a big leap up and that piece of the pie so one of the learning outcomes we had for this chapter is that we differentiate the difference we differentiate between rocks and minerals and minerals are basically naturally and naturally occurring substances that have a uniform crystalline structure and they're made of repeating elements of a particular kind that are going to make up that pure mineral now rocks are basically the assemblage of minerals so rocks can may be made up of many minerals but minerals are pure substances and those minerals as I mentioned are in crystal structures and the structures can be different they could be tetrahedral octagonal or octahedrons dodecahedron so all different kinds you might be familiar with quartz which is you know six-sided and you might see some rhombohedron x' which are are four-sided this is a calcite which has double diffraction so when you look through it has some optical physical properties to change the optics and make it appear as double vision and so we classify minerals based on several properties one of them is their crystal structure as shown here and one of the really cool things this is a salt sodium chloride on this side and if you ever I mean you've probably had seen salt but if you dissolve it in a glass and then slowly let the water evaporate out it will recrystallize but it won't recrystallize and these tiny little shapes you can actually get really big crystals that form back when the water evaporates out you can try that at home other physical properties of minerals include the color of the mineral but it's not very useful because a lot of very different minerals have the same color as you'll see in your lab that you'll do this week a lot of the rocks and minerals have similar colors so you can do color for some and narrowing it down but it's not gonna be the best one streak is the color it leaves when you scratch it on a porcelain tile so if you take a piece of porcelain it could you could be Earth's I guess ceramic tile ceramic tile is very hard and you would just take a mineral and scratch it along the tile and and the color of the streak that it leaves tells you a little bit about the identification of the mineral sometimes it's really cool the color of the mineral is different from the color of the streak that it leaves when you when you scratch it that that's pretty cool to see it look like one color and then scratch it and have it come out a different color the hardness of a mineral is also a way to classify a mineral they have different varying levels of hardness we could use the Mohs hardness scale and so one is the softest mineral like chalk talc and then diamond of course is the hardest mineral so it's on a one to ten Mohs hardness scale to a hardness of two could probably be scratched with the fingernail but then as you get up to the threes and fours we're talking about scratching pennies and then tile and of course diamonds will cut glass even so other properties that we use to look at minerals is whether or not they react with hydrochloric acid HCL and so their their ability to react with an acid is another way to analyze your properties some give off luminescent like a some Luminess they give off a little bit of a glow when you look at them with a blacklight and this there's really cool the Houston Museum of Natural Science has a really cool rocks and minerals exhibit including a whole wing under black light that has some really cool luminescence so we look at their Chris their structure or crystal form we can look at some other properties such as to the luster this is the way that they reflect light if they're glassy or metallic or dull so we can look at the way that they break and that would be their cleavage and the fracture if they break and irregular surfaces and of course density always helps to if we can get the mass and the volume of the mineral we can identify it so in order to form the minerals we're going to go back to our solution chemistry that we talked about in an earlier chapter what happens is we have these ions dissolved in water as we saw with calcium and carbonate and eventually that forms lime on the faucet around your kitchen sink that's a chemical precipitate and that's how a lot of these minerals form is through chemical precipitation so as the water evaporates you can get crystal ation crystallization and a lot of really cool structures now the rate of evaporation can affect the structure we get additional mineral formation when magma cools and Arak and and so for example and we had a little piece of rock with a gas bubble that was trapped and because of the way that it cooled it it would have been much more slowly and here and so we get more crystalline structure in there temperature pressure and time of course we're all going to affect the mineral forming process okay so rocks are basically a mixture of mineral so we talked about heterogeneous homogeneous mixtures earlier and we basically physically combined the minerals to make up the rocks most rocks are silicates and we're going to break those rocks into three major groups igneous sedimentary and metamorphic we'll talk about how they're formed and how they you know change forms through their rock cycle now first we're gonna talk about our igneous rocks and these are gonna form when magma or lava cools now the difference between magma and lava is really simple magma is underground and then once it reaches our surface we call it lava why the two names just to make it harder on you guys no actually they they go with their where they're found so magma would be lava underground so in magma cools were gonna form igneous rocks we've got obsidian here I've got a sample of that my collection it's really glassy and luster smooth pretty cool rock and basalt is another way igneous rock and granite those are some of the more common igneous rocks we basically classify the igneous rocks by their mineral composition in their texture and for any one more inch you know interested in a deeper understanding of the geology behind igneous rock formation you can take a look at some of the minerals that make them up and the elements that would make them up so that's igneous rock now igneous rock can be weathered and eroded and so all rocks can be weathered in rows sedimentary rock metamorphic rock igneous rock they're all weathered and eroded weathering can occur in several different forms chemical weathering which would just be like one of the biggest effects of chemical rather weathering would be acid rain the acid rain can dissolve the limestone and and pit it making it you know basically go away mechanical weathering like a physical process free-stall action where water gets in the cracks of rocks and then it freezes and as it freezes the water expands and so that can split the rock also biological weathering lichens that secrete weak acids on rocks as well as tree roots that help break up rocks can can break what rocks apart now the erosion is more about the transportation of that material wind certainly can wear away at rocks and transport material wave action is huge on on making really nice polish around smooth rocks on the shore mass movement like landslides rock slides mud slides that's gonna move a lot of material cause it tumbling down and and smooth out erode it and of course running water like a stream that's going to also erode rock down into smaller fragments and smooth it out as well so here we have a stream coming through and deposition is where material gets deposited and the fastest part is going to be coming around the bend so you can see in the dark blue section we're gonna have the fastest velocities and where it's fastest we're gonna have our greatest point of erosion so this is going to be a heavily eroded Bank and then it's going to zip around here and this will be a heavily eroded Bank on aside and it'll it'll run deeper through this area to its shallow or where you get deposition because it materials where it's going slower that it settles out and fills a little deposit but where the velocity the stream is moving faster it carries a lot of that material away and it'll eat away in a rode away at the the bank so you get erosion on this side and deposition on the slow side and remember that the deposition is because the stream velocities are slower so materials can settle out it would take a larger velocity to move larger material you wouldn't find for example a sandy bottom here because the faster stream velocities would pick that sand up and transport it you might find it over here instead or at the mouth of this river what happens over time is as you get an increase in velocity it can go so fast that it cuts away and slowly just keeps cutting away cutting away cutting away you get a huge storm come through it can actually push it and just skip this all together and that would geologically change and form what's called an oxbow lake where it was part of a bend of the stream but it ended up being cut off from the rest of the stream and there's plenty of oxbow lakes a famous one where I went to school in Louisiana Natchitoches cane river lake which is kind of funny in cane river lake but it was an ox bell looking at the cross-section of this river site a and B this transect along here you could see that B is going to be the eroded site and a is going to be the deposition site so your channel is going to be deeper closer to B as it's a roading away there's some quiz questions about that that's why I spent a little bit more time on that slide explaining it there's also a quiz question coming up on these features here saltation if you've had Spanish class salt ours to jump and so you know what happens is these materials heavier stuff doesn't actually get suspended it just kind of rolls and and that'll smooth it out and also round it out round it out and move it smaller materials and lighter that can take larger jumps and be bounced around along the bottom and of course any of the small particles like sand and silt and in other sediments they will be picked up and and carried with the current or with wind in this case if you're in a stream this is one of my favorite aquatic features Galveston Bay my old stomping grounds Houston College Station up the road Texas A&M and where I did my graduate work spent a lot of time studying Laguna Madre Corpus Christi Bay and but the reason why I'm showing you this is one the Trinity River will come in and you see all this sediment from the river loads that come into Galveston Bay and you can actually see it turned up and ultimately that will make its way out through this narrow inlet but you also have a barrier island formation along the most of the Texas coastline and any of you who take trips out to North Carolina you've probably been out to the barrier islands over North Carolina there's a couple of different theories of how barrier islands form but between the waves the currents and the material coming in you get you know barrier island formation this is a Delta so right there this is a Delta and this one is a famous one bird's foot and the Ganges the mouth of the Ganges in India and again these are barrier islands and they're great for protecting the coastline too because they act as an initial break for wind and waves this is a delta and these are formed by deposition also so material coming out will be deposited and raise that up you can also get oftentimes if this is land form and the water comes along and you're at the beach here you might swim out and it's really deep but you keep swimming and then all of a sudden you can stand up and you're pretty far off shore and that's called a sandbar and a lot of that happens similar to the barrier island formation so my point in telling you all of this is eventually we're gonna get to form our next piece rock we started with igneous rock and we talked a little bit about weathering and erosion but what's gonna happen next is that these sediments that are deposited from weathering and erosion are going erosion are going to compact and submit to one another they can be a chemical precipitate they can be kind of glued together and that process is called lithification and lithification is the process of becoming a rock and there's two main parts there's compaction that's gonna reduce the thickness of a deposit by smush as you know it squeezes out the water and so in the cementation that's the spaces in between they're gonna be filled with chemical deposits that help bind all the particles together and form sort of a conglomerate and that's gonna form our second type of rock rock a sedimentary rock this is the rock where you find fossils so you're not gonna find rules in igneous rock you're not gonna find it metamorphic rock but you will find fossils in sedimentary rock some of the most famous ones sandstone and limestone they're going to be the big ones conglomerates and limestone rock is another big one and it's just an accumulation of silt and sand and other materials that have been cemented and compacted together and that's why we can find fossils in this kind of rock because what happens are these ancient organisms would get buried and then through that burial process that they would preserve the fossil as the as the bones would begin to Litha Phi so metamorphic rock is going to form from intense heat and pressure we're gonna take existing rocks from sedimentary or igneous rocks or even other metamorphic rocks and we're gonna apply a tremendous amount of heat and pressure from within the earth and that's gonna transform the rock into a new type of rock it undergoes a physical change and so it is not same Rock for example if I take limestone and put it under tremendous heat and pressure I'm gonna change this sedimentary rock into metamorphic rock marble and so if I take sandstone I'll form quartzite and so we can get shale into slate and form different kinds of metamorphic rock what might cause metamorphic rock or this intense heat and pressure to be changed well it's gonna be what we'll talk about in the next chapter it's gonna be a geophysical process where crustal material gets moved and the temperatures are gonna get so high as we start to push rock material back down into the mantle that they'll melt they may not melt all the way down into magma they can but they may just partially melt and that's gonna cause a recrystallization and so that recrystallization process is going to form a new type of rock metamorphic rock and there's a picture of metamorphic rock same from the beginning of the slide show now one of the things that makes what metamorphic rock easy to point out are the ribbon like foliated layers foliation foliation is a vocabulary word from your chapter where you're gonna see folding and layers get bent up and twisted around and that's a great way to pretty much deduce that you've got some metamorphic rock now that's not to say that just because it has some folds that it is metamorphic rock but it's a great first guess before until you do further testing the last thing I wanted to talk about before the rock cycle are the evidence is that we have for Earth's internal structure now the deepest hole we've ever gone would be about what six thousand meters I think I'm not positive about that I should know I was working next door to the ocean drilling program for years but the everything we know about the interior of the earth is basically hypothesized we have a lot of evidence to Hort our hypothesis on what we think the Earth's internal layers are and I'll go through those and you can take a look at the evidence yourself but we're gonna take we'll start with Earth's magnetic field and look at it geomagnetism we because we know that earth is magnetized and behaves like a gigantic bar magnet as we talked about earlier in the course the only way you can really get you know that kind of magnetism is if we have you know an a liquid iron core on the outside where materials moving around the effects of gravity heat flow vibrations in the earth we're gonna all of these are gonna be pieces of evidence that tell us a little bit about the internal structure of the earth we're also going to infer we've looked at meteorites and and examined them and assuming that the rocks of meteorites are analogous to say this terrestrial planet that we live on we would have a solid iron a nickel core inside the liquid outer core but the biggest evidences are going to be seismic waves will look at p-waves and s-waves and those are gonna tell us a lot about the Earth's interior and as well as nuclear explosions that's provided a little bit of data - about the interior of the earth and you're gonna have to call back a little bit of information from your waves chapter when we talked about longitudinal compressional waves and two transverse waves so seismic waves there are two major kinds p-waves and s-waves P waves are longitudinal and they are much faster so they will arrive at a seismograph which is an instrument that measures seismic waves no way faster much faster than S waves which are going to be transverse P waves can move through both solid rocks and liquid materials there's not there will be a little bit of refraction as they change media but we're gonna be able to see that refraction with seismographs across the surface of our planet the S waves little slower think of s as surface waves and these are the kinds that you might see in apocalyptic disaster movies where you've got like an earthquake and you see a gigantic almost like an ocean wave traveling across the surface of the earth and these are they're gonna be the ones that caused the most damage to a city and they arrive a little bit more slowly than the compression waves and what's really interesting is they don't travel through liquids so they're not gonna go through our liquid outer core and that's gonna help us to infer about the Earth's interior so just to get started this is gonna be really helpful for the next chapter as well we're gonna start with the lithosphere the lithosphere is rock hard solid rock material so the lithosphere and that's gonna sit on top of the asthenosphere and I think there's a quiz question about that the lithosphere is gonna be on top of the asthenosphere there's this little layer in between the you know the lithosphere and the asthenosphere the Moho for short it's kind of where one meets the other the mantle is mostly most of the earth is mantle and this is going to be molten rock so you know the silicates that we talked about earlier mostly silica oxygen some nickel iron but it's going to be molten rock and the mantle and then it is way thicker than the crust and then finally we've got the core the core can be divided into two parts the outer core which is supposed supposedly liquid iron and nickel and the inner core which due to the pressure would be solid iron and there's some you know evidence to suggest to all of this that we've been talking about we'll do more on this slide in the next chapter I'm gonna skip this for now but there's two kinds of crust oceanic crust and continental crust they vary in density and thickness well again we'll hit that again in the next chapter when we talk about play techtonics let's skip this we already discussed the mantle makes up most of the Earth's volume it's gonna be molten rock but I want to show you this picture and this is the evidence that suggests a lot of the interior of the earth if we have seismographs which is an instrument that measures seismic waves earth you know waves in the earth if we look at P waves there's going to be an area there where if we had a seismograph here and and put a seismic signal right here at the star that there's this shadow zone where no P waves are detected and so that actually gives us a little bit of information since we know the diameter of the earth when it's it's sort of an oblate spheroid it's not perfectly spherical but we can estimate the size of the core based on the shadow zone we also know that when you get refraction there's a chain you get a change in medium there's a refraction and so we can also infer a little bit of information about the material of the core and so the way that the waves travel through that medium so these are P waves now S waves they won't even go through the course so we only get S waves on this band here and that's it and since we know S waves don't go through liquids then we can also assume that these that the outer core is also liquid and it's shown here the S wave ray paths do not go all the way through so int none of the seismograph on this side of the planet would pick up s waves from an earthquake over there and there's enough earthquakes going on all the time you don't hear about them because they're not devastating but if you subscribe to the USGS earthquake notification like I do you will be inundated with emails about seismic activity globally even you know all the way down to the 1.5 depending on how you set your alerts so a lot of information that we have to and for and support their harp our hypotheses about the layered earth again I mentioned we talked about meteorites and use them as analogies Earth's magnetic field we know that there's a turbulent flow within the liquid core because that's what's gonna be required to produce the magnetism we also know that Earth's magnetic north and magnetic south pole move around and that they've actually wobbled and and flipped right now we are due for a pole reversal a magnetic pole reversal the magnetic north is actually in the South Pole and the magnetic south is in the North Pole and of course you all know that because the north end of your needle points to the South opposites attract we have to update our navigation charts if you followed a compass and you're using navigation charts from 10 years ago you your magnetic north pole is gonna be off by a little bit it moves around so all of this is consistent with an iron core model we already brought up the term asthenosphere it's a elastic semi-liquid layer in the upper mantle it's kind of like not quite it's almost like a slushy it's it's not quite liquids not quite solid still kind of flows around a little bit so it's elastic semi liquid the lithosphere however if you remember that root word or lift though from lithification it means rock and so this is gonna be a solid layer of rock it includes all of the crust the Moho and a little bit of the upper mantle and it's made up of rigid plates that we'll talk about next chapter lastly the rock cycle we've already discussed it you already know it if you've been paying attention we have three kinds of rock igneous rocks sedimentary rock metamorphic rock and of course magma is molten rock of all the kind so we can cool magma and that will form igneous rock igneous rock can be undergo heat and pressure to become metamorphic or it can be weathered and eroded into sediment which can lift the phi in a sedimentary rock sedimentary rock can undergo heat and pressure to become metamorphic all three kinds of rocks can be weather an eroded sediment and all three can be destroyed and melted back down into magma so you've got a great lab ahead of you on the rock cycle and if you have any questions give me a call thanks