Exploring Rocks and Minerals

minerals and rocks let's get started so what is a mineral well a mineral is an inorganic naturally occurring solid that has a definite chemical composition and atomic structure now that's quite a mouthful let's break that sentence down a little bit for something to be classified as a mineral it needs to be inorganic meaning not living ever was living or composed of living matter or organic matter it needs to be naturally occurring meaning it can't be man-made additionally it needs to be a solid under normal conditions on our surface it has to have a specific definite chemical composition a unique Elemental makeup and a specific atomic structure here's some common minerals including this sample of potassium felds barar also known as orthoclase this sample of sulfur this sample of Musk Mica some Galina calite Olivine and quartz now one of our jobs is to be able to identify these minerals based on their mineral characteristics and here are some of the things you should look at the most obvious is of course color and that's sometimes useful for example in the case of sulfur which is a very distinctive yellow color however keep in mind that there are other yellow minerals and that many minerals come in a variety of color so color is not always the most reliable characteristic for identification we also look at hardness using the mo scale of hardness with one being the softest mineral and 10 being the hardness what we will often do is take a piece of glass which has a hardness of 5.5 and try and scratch it with a mineral sample if it leaves a scratch that means the mineral is harder than the glass we can also look at luster the most simple luster is metall metallic or non-metallic streak would be the color of the mineral in its powdered form and we would test that using a streak plate finally we can take a look at how the mineral breaks if it breaks predictably we refer to it as displaying cleavage if it breaks randomly it displays fracture there are also some other characteristics like is it magnetic does it have a taste or odor does it Glow in ultraviolet light does it bub with acid as well as a variety of other things that we can look at so let's take a look at the New York State earth science reference tables this is the properties of common minerals chart let's see how it works it's very simple here's the column for this mineral Galina and you can see from left to right left to right it tells us it has a metallic luster it's very soft with a hardness of only two and a half it displays cleavage and a metallic silver color has a gray black streak and it's very dense is used as an ore of lead and in batteries and is composed of lead and sulfur here's another example this is Olivine you can see it's a much harder mineral displays fracture it's non-metallic and can be used in jewelry and you can see its chemical composition right there so those are minerals now what happens when minerals combine in nature well we get rocks so minerals are the building blocks of rocks now of course there are thousands of types of rocks on Earth and so we need to classify them and so we've come up with a classification system in which rocks fall into one of three types of rock and that classification system is based on the way in which the rocks form the three groups are as follows ous rocks from magma or lava sedimentary rocks from compacted sediments and metamorphic rocks exposed to intense heat and pressure so let's begin by looking at ous rocks as I mentioned these are rocks that form from the cooling and solidification of magma or lava let's take a look at the reference table on ignas rocks so if we zoom in these are our 17 ous rocks shown in bold and you'll notice that there a whole bunch of characteristics shown on this chart so let's go through them a little bit we begin with these top rock which are referred to as being extrusive or volcanic and that simply means that lava erupted on Earth's surface and cooled quickly forming these rocks now because the lava cooled quickly mineral crystals within it were not able to grow very large at all and so what we see are that some of these rocks formed from lava have a fine texture with crystals that are less than 1 mm in size like this sample of Basalt or this sample of riight notice the crystals are very small almost impossible to see we also have rocks that cool so quickly that the crystals are impossible to see in fact they're non-crystalline or glassy rocks like this obsidian sometimes lava cools quickly enough for little air bubbles to be trapped inside these rocks are referred to as being vesicular like this sample of pmus right here but what about when magma which is lava just inside the Earth takes a long time to cool because it's so hot inside the earth well in that circumstance we get intrusive ous rocks some of these intrusive ous rocks will cool slow enough for the crystals to grow in the magma deep under the ground between 1 and 10 millim in size like this sample of granite notice how the crystals are much larger and clearly visible with the naked eye sometimes if the magma cools very slowly the crystals will grow even larger over 10 mm in size like this sample of pegmatite notice those large biotite crystals now let's Zoom back out and see what else the chart tells us this Center area shows us color the rocks on the left side are lighter in color and on the right they're darker here's density the left side they're less dense and the right are more dense and here's composition the left side are felsic meaning they're rich in Silicon and aluminum and the right side are maic rich in iron and magnesium finally the bottom of the chart shows us mineral composition the way we read this is we simply find the ous rock we're interested in like say pegmatite and we look down beneath it to see that it commonly contains these minerals potassium felspar quartz plag biotite and ampol similarly we could look over here and see that Basalt or diabase or gabro contain other minerals like pyxine and Olivine and so that's how we read that chart but there's another chart in the reference table seen here called The Rock Cycle that also shows us a little bit about ous rocks namely that they form from melting into magma and then solidification so as you can see there's a lot of useful information about ignas rocks around right in the earth science reference tables again just to review intrusive ignas rocks have large crystals because of slow cooling extrusive ous rocks have small crystals or maybe even no crystals because of fast cooling some of these extrusive rocks may be crystallin or glassy and others could have air bubbles or be called vesicular now just a quick reminder that the longer the cooling time the greater the crystal size the larger the crystals will grow and so that's what you need to know about ous rocks but again we've got two other types to look at sedimentary and metamorphic let's talk about sedimentary for a minute now these are rocks that form from the compaction and cementation of sediments keep in mind that sediments are just bits and pieces of other rocks the other rocks could be any kind but if the right conditions exist bits of rocks may be squeezed under the pressure of water and then glued together with this sticky mineral glue so let's take a look at our New York State reference table on sedimentary rocks notice it's broken into a top and bottom portion let's begin with the top here these are referred to as being clastic rocks which simply means rocks that as I mentioned are made of compacted and cemented sediments and it's very simple each rock is just made of a different combination or size of sediments let's go through them this is a conglomerate conglomerate is made of big and small sediments mixed together as long as those sediments are rounded it will be classified as conglomerate if those sediments were angular I would have a breia seen here again a mixture of large and small sediments keep in mind we don't care what these rocks are we don't care what the mineral makeup is as long as it's a bunch of different things compacted cemented together then we have a sedimentary clastic Rock if the rock is made of sand siiz sediments appropriately enough we have a sandstone smaller sediments called silt will give us a silt Stone and smaller still called clay will give us a rock known as shell and so those are our classtic sedimentary rocks but we do have some other types of sedimentary rocks some of them are called crystallin like this rock salt now this is a rock that forms when you have minerals like in this case halite dissolved in water and then that water is given time to evaporate when it evaporates Ates the water leaves but the crystals of the minerals that were dissolved in it stay behind and you're left with something like this rock salt we also have uh other types of crystallin or other sedimentary rocks for example this sample is something called Limestone we refer to Limestone as being bioclastic now remember our clastic rocks were set in stuck together so our bioclastic rocks will be Biol LIF living thing stuck together in this case we have shells stuck together this is called a coina it's a type of limestone another example of a bioclastic rock would be bituminous coal which is made from compacted remains of plants and so those are our sedimentary rocks and again take a look at the rock cycle because it sums this up nicely you'll notice we need some processes to happen for example we need existing rocks to be weathered or broken down and to give us sediments those sediments can be eroded or moved and then deposited or dropped off and then buried by other sediments and that weight providing enough pressure and compaction and cementation for the form for the formation of a sedimentary rock so just a review clastic sedimentary rocks are classified according to the size of the sediments that make them up crystalline sediment rocks like this rock salt are formed from the evaporation or precipitation of minerals in water and then finally we have bioclastic sedimentary rocks like this Limestone and coal these rocks are formed from the compaction and sediment cementation of organic matter so back to our rocks we have our ignas sedimentary and one more group to look at metamorphic rocks so metamorphic rocks are formed from exposure to int intense heat Andor pressure you can take any kind of existing Rock and if it gets forced down by the motion of tectonic plates into the Earth's crust intense heat and pressure down there will cause it to change or morph into something new here's the New York State reference table for metamorphic rocks again you notice there's quite a variety and a large list of characteristics in information here let's take it bit by bit the top section are referred to as being foliated rocks and these form primarily from regional metamorphism which is primarily a result of pressure so I give you an example of a typical scenario that occurs in nature we start with this rock which is known as Shale now you may recall this this was actually a sedimentary rock made of very small clay-sized particles well shell which is very common on the Earth's surface might get forced deep underground by the movement of tectonic plates and under those conditions the shell would be exposed to increased heat and pressure and it would be morphed into a rock called slate notice they look very similar now if that slate get gets pushed deeper underground it will metamorphose even more and become something known as fite even more heat and pressure and we'll get a sample of shist and even more and we will get the rock nice notice the bands in nice that's a very common characteristic now if a sample of nice is pushed even deeper on underground the heat and pressure will actually cause it to melt and then it will become an intrusive ous rock so this is a result of increasing heat and pressure within the Earth's crust so those are our regional metamorphism rocks notice something they are all referred to as being foliated and what that means is that pressure is causing the minerals within the rocks to almost line up with each other now we have two types of foliation we have mineral alignment seeing here which is when minerals line up as a result of pressure and then a severe version of mineral alignment is called banding seen here the only rock that displays banding is called nice and this is a result of really intense pressure but we also have these nonfoliated metamorphic rocks some of which are still caused by pressure like anthy coal right remember regional metamorphism is from pressure we'll take a look at that in a moment some of these however are caused more by heat something called contact metamorphism when The Rock comes into contact with really intense heat from lava or magma nearby and then of course some could be a combination of heat and pressure or heat or pressure let's take a closer look at this first one the coal now if you recall there was a sedimentary rock known as bituminous coal well if you take bituminous coal and you had intense pressure it will metamorphose into a new rock that looks similar but is much more dense this is called anthy coal and it is a metamorphic rock this same idea can actually happen to other rocks like this sedimentary rock Sandstone which we mentioned earlier now if you add intense pressure and heat to that or if it comes into contact with Magma then it will be affected by that heat and it will metamorphose into a rock known as quartzite and you can see that right here on the chart notice it actually says metamorphism of quartz Sandstone the same thing would be true underground notice we have some layers of sedimentary rock here maybe one of those is sandstone and then one day a magma intrusion forces its way up and wherever the magma touches the other Rock it's going to cause some contact metamorphism that's where you would find your Quartzsite or your hornfels or even a rock like marble or metac conglomerate all forming from contact metamorphism so those are our metamorphic rocks keep in mind that the key characteristic to look for with metamorphic rocks is banding you will not see banding in any other type of rock other than metamorphic again let's look at the rock cycle in the Earth's crust and you'll notice that it clearly shows that metamorphic rocks are formed from intense heat and or pressure and so again you see this whole rock cycle comes together where any type of rock can be affected by changes that will turn it into any other type of rock ignas can be weathered and turned into sediments which can become sedimentary rock ignas could also be exposed to heat and pressure turning it metamorphic ignas could even melt and form a new ous rock and so that's how the rock cycle works rocks have been continuously changing from one type to another throughout the history of the Earth that's about it for rocks and minerals thanks for listening

Channel: Mike Sammartano

Views: 1,293,480

Keywords: Rocks and Minerals, Rocks, Minerals, Earth Science Reference Tables, ESRT, Obsidian, Intrusive Extrusive, Clastic, Geology, Earth Science

Id: ZkHp_nnU9DY

Length: 17min 4sec (1024 seconds)

Published: Sun Feb 08 2015