howdy everyone and welcome to our final video of module three where we will look at our last type of rock are metamorphic rocks metamorphic rocks are formed when pre-existing rocks are subjected to intense heat and or pressure and this causes those rocks to alter or change into another rock or metamorphos into another rock that we call metamorphic now there are two different types of metamorphism we have contact and regional metamorphism which we'll get into here in a moment and how we tell the type of metamorphism depends on how the grains are aligned so we classify metamorphic rocks based on how the grains are aligned we call them foliated or nonfoliated rocks so let's take this rock for example does anyone recognize this rock pink crystals big crystals this is a felic intrusive ignous rock this is granite right if we put granite under intense heat or pressure underneath the earth's surface we we squish it all of these grains that you see here are going to align themselves based on the direction of pressure and recristallize see we have dark and light colored bands this is called foliation foliation is the alignment of minerals so this would be a foliated metamorphic rock and foliated metamorphic rocks are created by regional metamorphism which is where we have intense pressure intense pressure think large regional processes like plate tectonics plate tectonic boundary nonfoliated is when we don't see the mineral grains aligned and non-foliated rocks are formed by contact metamorphism which usually just involves intense heat no added pressure needed and we'll see both of those more examples here in a moment now metamorphic rocks again two types of metamorphism we have regional metamorphism which involves high pressure high pressure so these types of metamorphic rocks are usually found near plate boundaries like a subduction zone here here we have a foliated rock a lot of compression squishing this rock and it actually causes the mineral grains to realign themselves recristallize and preserve some of that deformation in its structure so that's a regional metamorphic rock and it is foliated this is nice this is a rock called nice but not all rocks need pressure to change sometimes we just need a lot of temperature a lot of heat this is called contact metamorphism contact metamorphism quite simply means it's in contact with something super hot think like a magma chamber all the rocks around the magma chamber the ones that don't melt because metamorph metamorphism does not involve melting if it melts we're in ignous territory but the rocks that don't melt that just get superheated they get baked like a cake and they create nonfoliated rocks like a quartz site here those are rocks that are getting baked and recristallized because of the intense heat so regional metamorphism involves high pressure creates foliated rocks contact metamorphism involves high temperature creates nonfoliated rocks so metamorphic rocks come from pre-existing rocks so we call the pre-existing rock the parent rock so for example we have shale shale is a sedimentary rock if you put shale under intense pressure it'll change into something called a slate which is a foliated rock granite put it under pressure turns into nice basalt put it under pressure turns into shist or oceanic crust put it under pressure turns into shist now limestone you cook limestone put under intense heat it's going to change to marble that's a nonfoliated rock sandstone's a sedimentary rock if you cook it it's going to change to quartzite it's another nonfoliated rock so the parent rock needs a change in heat and pressure that causes it to create a new texture and it will become a metamorphic rock so this is slate this is what slate looks like this comes from shale that sedimentary rock that gets put under a lot of pressure and it changes the texture we see these clay mineral they start to line themselves up very sheetlike and create slate slate is what chalkboards used to be made out of although not a lot of schools even use chalkboards anymore this is nice this is what happens to granite when you put it under pressure all those minerals are going to line themselves up they're going to segregate themselves based on color and shape and we see those beautiful bands nice is probably the best example of a foliated metamorphic rock this is shist you put basult under a lot of pressure it's going to do the same thing it's going to recristallize and segregate themselves based on shape and color and you see these beautiful foliated bands we can also get shist from shale so shale turns into slate but you can continually put slate under pressure and it will change into shist shist is really cool it kind of looks like fish scales this is what happens to mudsiz minerals when you put it under a lot of pressure it actually starts to grow and form these platey um minerals called micas that stack themselves up like playing cards now this is marble marble comes from limestone when you put limestone under intense heat and pressure you've probably seen limestone before limestone makes up a lot of building material and then quartzsite is from sandstone being baked looks very similar to marble but they have different physical properties now the difference between quartzsite and marble is that marble comes from limestone it's made up of calcium carbonate calcium carbonate reacts easily with acid if you remember from the minerals lecture video so that means our marble countertops will react to our cleaning solutions over time they will get dissolved over time you have to be careful with what you use to clean marble but calsite that is in limestone and ultimately in marble is also a softer mineral it's not as hard as quartz and quartzite so marble also scratches easier so you have to be careful when you're cutting on marble countertops which is why I'm here to pitch the idea to you that quartzite is a better alternative to marble countertops and flooring quartzsite is more resistant to weathering more resistant to cleaning solutions and it's more resistant to scratching it's going to last you a lot longer than your marble will now here is the metamorphic continuum this just quite simply states that if you continue to put a rock under intense heat and pressure and you continually increase the pressure and the heat it's going to continue to change until of course it melts and then it becomes ignous so our shell you put under intense heat and pressure turns into slate you keep increasing things turns into phite keep increasing things turns into shist keep increasing things you can change it into nice so it's going to continue to change as long as you continue to increase that temperature and pressure all right so let's practice metamorphic rocks let's start with this boring rock here on your left remember we classify metamorphic rocks based on foliation their texture is this rock foliated or is it nonfoliated this is very easily nonfoliated we don't see any alignment of minerals whatsoever so what does that mean it's a non-foliated metamorphic rock how did that happen contact metamorphism remember nonfoliated is contact metamorphism and what is contact metamorphism means it was in contact with something very hot right now what if I told you that this rock reacts with acid you might say "Oh I remember that's calcium carbonate calcium carbonate is in limestone." Limestone that gets baked in contact metamorphism is going to change into marble so this is a marble and if I was on a hike and I came across marble what would that tell me well that would tell me that there must have been something really hot nearby to form this rock and maybe there still is today or maybe there was in the past like a superheated geyser a magma chamber something really hot was nearby to cook this rock all right now let's look at this rock over here on the right is it foliated non-foliated hopefully you can see right away the foliation in bands you see it's segregated by color here these bands so what does foliated rocks mean what does that mean it means it was formed by regional metamorphism which is intense pressure think like regional tectonic processes subduction zones maybe okay so this is this is a nice Okay nice has those very nice looking foliation bands we know it's foliated so we know some kind of regional metamorphism a lot of pressure plate boundary nearby so if we're on a hike let's say we were in the Appalachian Mountains came across this rock what would that tell you oh wow there must be a plate boundary nearby but wait a minute there's no plate boundary in the eastern United States well there's no plate boundary anymore the Appalachian Mountains were formed when um Pangia first formed when the continents collided and it formed the Appalachian Mountains so we did have subduction zones and we did have collision zones that created the nice that we're looking at today in the Appalachian Mountains so again you were able to tell me a really cool story just by looking at rocks again amazing and that brings us to our rock cycle we talked about ignous rocks we've talked about sediment and sedimentary rocks we talked about metamorphic rocks in the magma a little bit and we'll talk more about magma when we get to volcanoes but hopefully now this whole rock cycle makes a little bit more sense to you and how material of the earth is constantly constantly recycled throughout time so that brings us to the geological cycle again we talked about the tectonic cycle and this entire module talked about the rock cycle the ignous portion of it the metamorphic portion of it and even the sedimentary portion of it well thank you so much for sticking with me through all of module 3 i look forward to meeting you in module 4 where we get to our first disaster of the semester in earthquakes see you there guys