Welcome everybody to our Chapter 3 video lecture for Geology 101, Physical Geology. In this lecture, we'll be looking at minerals. In particular, minerals like that of the emerald you see on this title slide.
We, over the course of this lecture, will talk about what is a mineral. How do we describe them? How did they form?
And most importantly, how are they different from rocks? Very often when I teach this lecture, the first inclination of many students is to use the word minerals and rocks interchangeably. We will see over the course of this lecture that minerals. have a very narrow definition. They're very specific materials.
And when they come together in different formations and under different processes, only then will they form rocks. This will be important as we move through the rest of the semester talking about different rock types, etc. We have to start with minerals. But before we can get into looking at pretty and fun samples.
we have to do a brief chemistry review. For many of us, chemistry may have been months, years ago now, so it never hurts to just kind of go back and touch on the basics. When we look at all of the materials throughout our universe, whether it be big, like a car, an apple pencil, things we can see with the naked eye, or small water molecules at their, you know, most finite.
kind of shape. All of these things are made up of matter. Matter is anything that has mass and occupies space.
So it can occupy big space like a car or a planet, or it can occupy, you know, the basically atomic level, microscopic level. And depending on the characteristics of a given matter, we can group it into a state or phase. The first three phases or states are probably familiar to you. Solids, liquids, gases. If we think about H2O or water at its solid form, we have ice, liquid, we just have regular old water.
And then the gas would be water vapor. What comes out of your tea kettle or what comes out of your pot when you heat up that water. There's also a state of matter called plasma.
we're not going to talk about that at all today. In fact, we're really going to focus on the solids. As we will see, solid is a key part of the definition of a mineral. All minerals must be solid to fall under that kind of broad category.
So no minerals are liquid, no minerals are gases. All states of matter are made up of materials, elements. I gave the example of water.
Water consists of H2O, right? That is two hydrogen atoms for every one oxygen atom. So all matter on earth is made up of elements and at the smallest level, elements are composed of atoms.
So on this screen here, is the periodic table of elements. Perhaps you are familiar with this periodic table. We see things that are probably familiar like oxygen, helium, neon, iron, potassium, sodium.
These elements are found in many different materials. All elements at their smallest level are composed of atoms. What do atoms look like? The structure of an atom is pretty much the same. There will be some variability in terms of the number of particles, the subatomic particles, subatomic particles, the number can change, but the structure is relatively the same.
In all cases, an atom is that smallest unit of matter, right? Can't be divided in half any further. that smallest unit of matter that contains the characteristics of a particular element.
So for example, the element of oxygen has an atomic number of eight. It will look like this at its model. It is the smallest unit of matter.
We cannot break that oxygen down any further. And it will not, you know, if we did lose an electron or break it down, it would no longer be oxygen. It is the smallest unit of matter that contains those similar characteristics.
For each atom, there are a number of subatomic particles that change from element to element. If we look at the hydrogen, helium, and oxygen examples at the top of this slide, we can kind of see those differences. In the center of each of these examples is the nucleus. Protons and neutrons are the subatomic particles that are contained within that nucleus. Protons will be positive in charge, whereas neutrons are neutral, meaning no charge.
Surrounding that nucleus are negatively charged electrons. So, oops, I am so sorry. You see there in the yellow, those are the negatively charged materials orbiting around the nucleus. So they will have a negative charge. of these elements, you see that I've made a note of the atomic number.
For hydrogen, it is one, helium, it is two, oxygen, it is eight. The atomic number describes specifically the number of protons found in each nucleus. So in every sample of oxygen, there will be eight protons always. In hydrogen, there will be one.
proton always. And we can use those number of protons to create or construct the periodic table of elements. So going back to the figure we've seen before, you can see each of the elements is given by its symbol, which is a one to two letter designation on the periodic table. And then above it is a number. That is the atomic number, the number of protons.
And the periodic table is structured so that the number of protons increases going from one, two, three, four, and so on. So if we looked at a sample of iron, we see that it has the atomic number of 26, which means that it contains 26 protons. So our protons help define the material we're looking at. If we change the number of protons, we're changing our element. Neutrons are a little bit more flexible.
If we change the number of neutrons in a nucleus, we're not changing the element, but we are creating what is called an isotope. So on the slide here, you see three samples of carbon. These are three carbon atoms.
In all cases, they have six. protons, because by definition, carbon has six protons. They are indicated here in the, excuse me, in the center of that nucleus. We're not changing that number of protons, but as we go from carbon 12 to 13 to 14, we are changing the number of neutrons, creating an isotope. On the far left, We have six protons.
We also have six electrons there in blue. If we look down here, we see there are also six neutrons. We call this carbon 12. This is stable carbon and it is carbon 12 because six protons plus six neutrons equals 12 particles or an atomic mass number of 12 within that nucleus.
If we start to change the number of neutrons in particular, Here we're increasing. You can see in the center, we've now have seven neutrons, meaning there are 13 total particles in that isotope in the nucleus specifically. On the far right, we still have six protons, six electrons, but now we have eight neutrons, meaning that there are 14 total particles within that nucleus, giving us an isotope of carbon-14.
So the protons Don't change. In an isotope specifically, the protons are not changing here and the electrons don't change in an isotope. At its core, an isotope occurs when there is a different number of neutrons within that nucleus. When we have different materials bonding or joining together, we can create some more complex. materials.
I've already used water, H2O, as an example. In this case, hydrogen atoms have joined together with an oxygen atom through bonding. If we look at the figure in the center of the slide here, you see two kind of gray oxygen, or excuse me, two gray hydrogen atoms bonded to a red oxygen atom.
When you have two or more elements bonded together, that is when we get a compound. So H2O is a compound. Something like oxygen gas or ozone, not considered a compound because there's only one element present. They're still bonding. It's just not an element because it's very one-sided, just one element.
And depending on how these materials bond together, how they combine, we will see different behaviors. And when we look at minerals, we will see that there are two key types of bonds that help build minerals, construct them at their atomic level, and also help them break apart. So for the last part of our chemistry review, we will make the distinction between ionic and covalent bonding. For ionic bonding, the key word here is transfer.
Electrons from one element are transferred or sent to another one, like sending a letter. Common example of this is shown on the right side of the slide between sodium and chlorine. The sodium atom in an ionic bond will transfer.
an electron over to chlorine. In doing so, after the transfer, what is left? The sodium ion will have 11 protons and 10 electrons, meaning that it has a net positive charge.
It has one more plus than minus. If they were both 11, it would be balanced, but because there's one extra proton, it has an overall positive charge. As the electron is transferred to chlorine, it accepts that electron, meaning that it has, after the transfer, 17 protons and 18 electrons, meaning that it has a net negative charge. The positive and negative charges on these materials become attracted to each other, and they will form a bond creating sodium chlorine. or table salt.
So all of this takes place because of the transfer of one electron, allowing these materials to become bonded together. Covalent bonds are another type of bonding that we will see in minerals. When we have H2O, the bond between H and O is a covalent.
bond. In this case, there's no transfer, no transfer. Instead, we see sharing.
The outer electron rings overlap with one another. As they overlap, the individual electrons can become shared across two different elements. This is a covalent bond.
So there's no transfer or changing of the charge, simply just some sharing between atomic friends. That's it for our chemistry review. Not too bad, right? Not too bad.
We're going to use these ideas, though, as we walk through our discussion in minerals. So we have to keep these things in mind, and that is why it is fair game for the exam and why it will have questions on the homework, etc. But now to the fun stuff.
Now to minerals. At the end of this lecture, you're going to be able to rattle off the definition of a mineral with your eyes closed. Minerals are naturally occurring in organic crystalline solids with a defined chemical composition and distinctive physical properties.
I know it's a mouthful. We're going to go through it one by one. But this is what I meant on the title slide when I said that minerals have a very narrow definition.
In order for a material on Earth to be a mineral, it must check every single one of these boxes. I'll give an example of how specific this can get, especially when we get to point number two. But it's important to start at the top, so we will begin with naturally occurring. Naturally occurring means occurs in nature. No man-made substances will be found in the mineral category.
We've gotten better at creating things in labs for sure. We're seeing lab built or lab created gemstones as well. But for the mineral definition, we need these materials to occur in nature. The second point is inorganic crystalline solids.
We're going to do this one word at a time. inorganic means not living it's not made up of stuff that was alive or is alive inorganic no animals or plants are harmed in the creation of a mineral now plenty of living things use minerals for example corals clams especially like little sea critters can use minerals to construct coral reefs shells things like that. But at its core, a mineral is not something that was or is ever alive. Crystalline means that it has a defined chemical composition, as we'll see in number three, that the atoms will bond together in a three-dimensional structure. And some of times that can give off a crystalline shape as well, a prism or...
pyramid shape as those atoms bond together. And the last point is solids. Going back to our phases of matter, we compared solids, liquids, gases, and I said at the time that solids are the only phase of matter that can be considered in the minerals. To show how extreme this definition is, I want to compare ice and water.
liquid water. Ice is a solid. Water is a liquid. Ice is naturally occurring in organic crystalline with a defined chemical composition and distinctive physical properties. Ice is a mineral.
Yay. The only difference between ice and water is that liquid component, but it's not good enough. Water is not going to be a mineral because it is a liquid.
That singular change from solid to liquid means water gets the boot. So it must be a solid to be considered a mineral. Defined chemical composition. I mentioned this very briefly when looking at the word crystalline. All minerals will have a very specific composition, elemental composition.
what they're made of. For example, the three minerals on the right here, feldspar, quartz, and biotite, all have some similarities in their atomic structure. These atoms will also arraign themselves in a specific way. When we look at what feldspar, quartz, and biotite have in common, we will see that the three-dimensional structure of the compounds are very similar in shape across these three minerals. That's why I chose these three minerals, because they look very different on the outside, but according to number three, they are very, very similar on the inside.
And that also ties into distinctive physical properties. If I were to ask you to define the three minerals on the right side of the screen, you'd probably start with color, shape, right? What you would perceive it feels like.
These three minerals are very distinct from one another, but they do have similarities in their chemical composition. We will see over the next few slides that these minerals fall under the silicate's umbrella, which means that their chemical composition is so similar that they are grouped together. It is only their distinctive physical properties that really set them apart, even though at the smallest level, they're very, very similar.
And as I said on the title slide, we are going to make a very big distinction between minerals and rocks. Minerals are the building blocks of rocks, meaning that they come together in a number of ways to form rocks. When we talk about the rock cycle in our next video lecture, you'll see that rocks are kind of grouped according to how they form.
And when these minerals are put together in a number of unique ways, they will form a rock. So feldspar, quartz, and biotite, the three minerals from the previous slide, when they are put together in maybe a magma chamber deep in Earth's interior in volcanic process, they can solidify and form granite. So granite is a rock because it is a combination of three or more minerals in the case of granite.
So minerals are the ingredients. Rocks are the soup. You have your three ingredients.
They come together and make something new. When we talk about the crystalline solid part of minerals, I think we can mostly imagine what I'm talking about when I talk about crystals. We often associate the word crystal with what a mineral looks like, and that is fair. You can see a number of geometric shapes or crystals here on the screen.
But this, again, is tied to the 3D composition of those atoms, how they bond together. The differences in bonding, the strength of those bonds allow these minerals to take on these flat or planar surfaces that are smooth with sharp corners or straight edges. And there are a number of different crystalline shapes.
Many people, when they think of crystals, their mind goes to the prism shape on the far right there. But of course, that is far from the only crystalline shape that we see in nature. We have cubic, kind of the spherical, or the diamond pyramid shape. They all have in common these three characteristics.
Flat edges, sharp corners, straight edges. Now, Mother Nature is messy, so not all minerals are going to come out perfectly prismed and beautiful. But even with the kind of messiness of nature, for example, if we look at this sample of quartz, you can still see the rough edges of a prism.
It's not perfect. It's not exact, but it's close enough that we can use this crystalline shape to categorize the minerals and describe how. their atoms form together or bond together. Another key part of the definition of a mineral was the defined chemical composition.
Now on this slide, I've added an extra word to that, narrowly defined. And that goes back to what I said on the previous slide, which is mother nature can be messy sometimes. So minerals they have some flexibility in their elemental composition, particularly when it comes to things like iron and magnesium.
These elements are very similar in size. They have a similar charge. So it's not hard for these elements to swap in and out with each other. So in one place, you might have an iron rich biotite.
In another place, you might have a magnesium rich biotite. They're the same mineral because we say narrowly defined. We allow for some wiggle room, especially when we have these ions that are similar in size and charge.
So it's narrowly defined. Basically, that means there's a teeny tiny bit of wiggle room. For the most part, it's pretty well defined. But if there's iron or magnesium present, we'll allow for some kind of variation there because that's common in nature. Now there are thousands of minerals on earth.
um estimates are upwards of 3,000 to 4,000 but of the minerals that we study especially in this class geology 101 there's only about two dozen or so that are really really common um if you go on to be a geology major which would just delight me you take an entire semester-long class studying mineralogy so that's how involved the study of minerals can be an entire semester's class, right? Some people dedicate their career to it. This is one-on-one.
We have one chapter. So we're just going to touch the surface of the two dozen common minerals, something that they all very frequently have in common is their elemental composition in particular, silicon and oxygen. Silicon is SI, oxygen is O. These two elements make up the majority of our crust. We have two pie charts here on the bottom of the slide that illustrate just how much of the crust they compose.
By weight, oxygen makes up nearly half of the Earth's crust, whereas silicon is just a little bit under 30%. And if we look at the number of atoms, the... oxygen, number of oxygen atoms at nearly 63% is almost two thirds, whereas silicon is about one fifth. And if we look at these power charts, no matter how you kind of crack this egg, the oxygen and silicon make up the bulk of the elements.
And so they are going to be the most common elements found in minerals, just because they're abundant, they're everywhere. And when silicon and oxygen bond together, they form what we call a silica ion. It's shown here on the top right of the slide.
You have a small brown silicon atom surrounded by large red oxygen atoms. For every silicon atom, there are usually four oxygen atoms bonded to it. And it sits in like a little pyramid with three atoms on the bottom, one oxygen on the top with the silicon in the center. When we group together our minerals, we use that information.
We use things like silica to describe these mineral groups. So depending on the types of elements found in a mineral, we group them together. This is called grouping by radicals, mineral groups by radicals.
So silicates, as I introduced on the last slide, again, have one bonded silicon atom to three, or excuse me, four oxygen atoms. and minerals that contain this silica bond are called silicates. Now these are going to be the most abundant type of minerals, but there are other groups.
I'm showing some here, carbonates, sulfates, hydroxyls, but silicates are going to be the most abundant and what we spend the most time talking about today. But what's important to take away is that we group together our minerals based on their radicals, based on... what they are made of. So this is why we had to have our chemistry review.
We needed to discuss how mineral or how, excuse me, elements bond together, how we describe our elements, right? What they're called, how we organize them in order to understand how we group together our minerals. This is just a table from your book, just to illustrate that there are several mineral groups.
Again, we're really going to focus on silicates today because they are the most abundant, but if you were to take a mineralogy class, you would become incredibly familiar with carbonates, phosphates, sulfates, sulfides. The other mineral group I'd like to point out here are called native elements. There are a number of elements on the periodic table, like gold, silver, or even diamonds that are composed of simply one element.
So gold, silver, diamond is just formed of carbon. These are the native element minerals. They're just formed in nature. They don't have any radicals. They're just made up of one type of element, but still important.
So again, 95% of earth's crust is going to be made up of these silicate minerals because we learned that silicon and oxygen. together make up the bulk of the Earth's atoms by weight and by number of atoms. And when these silicon and oxygen atoms bond together, they form what we call a tetrahedron here. It's just like a little pyramid. You can see it kind of expanded on the bottom right.
We have four oxygen atoms. We have one silicon atom at the center, creating this little pyramid, a specific three-dimensional chemical composition, which again is key. to the definition of a mineral.
And so all minerals that contain this silica tetrahedron fall within the group of silicates. Now they can contain other materials. The two types of silicates really illustrate this well. There are ferromagnesian and non-ferromagnesian silicates. Let's figure out what the word ferromagnesian means.
Ferromagnesian gets its name from two elements, magnesium, magnesium, pretty straightforward. The ferro is a little trickier. It's iron.
Depending on the type of silicate we're looking at, if it contains iron or magnesium, as well as the silicate mineral. or excuse me, this silicate radical, we call it ferromagnesian. Non-ferromagnesian means that there is no iron and there is no magnesium present. So the presence of iron and magnesium, heavier metal elements, would they be considered darker or lighter? Think about metals.
The presence of iron and magnesium will make our silicates darker in color. So pyroxene is an example of a ferromagnesian silicate. It contains, again, that iron or magnesium, giving it that darker shade. Whereas a non-ferromagnesian silicate, like quartz, does not contain iron or magnesium, and therefore it maintains its lighter color.
Here are some samples of ferromagnesian silicates. They're largely dark. Olivine is kind of the exception, not the exception, the standout.
It's made up primarily of these very green colored crystals. That's why it's got the name Olivine. It can be grayish in tone as well. When we look at non-ferromagnesians, you'll see that Olivine really fits in better here anyway, especially because it does contain. iron or magnesium.
These in general are very dark in color and are going to be denser than non-ferromagnet silicates. Again, because they contain these metallic materials causing them to be denser. Non-ferromagnet silicates again mean that there's no iron or no magnesium allowing them to maintain a lighter colored composition. You can see quartz. potassium feldspar, plagioclates feldspar, all lighter in color.
And they are less dense than ferromagnesium silicates because they do not contain those heavier metal materials that we would expect. I know I said we were just going to focus on silicates, but again, I want to tie in this idea that, yes, we will see minerals falling in other mineral groups. Here are just some images.
In particular, I like to show gypsum and halite because they both are kind of clear, transparent, crystalline. You might see how it could be easy to confuse them for each other if you're not sure what to look for. That's, again, why we group them according to their mineral composition.
Galena on the bottom right is a sulfide. It's very dark in color, very metallic. It's also very dense, very heavy.
So again, these are grouped according to their mineral or their elemental composition. These are not silicates. These are just other examples.
So one of the last key things to talk about when we discuss minerals is how we can identify them, because you can imagine that if you're out in the field. You may not have a piece of equipment that will allow you to quickly identify the elemental composition of a mineral. You take it back to the lab, you might be able to identify it as a silicate.
But on your own in the field, it's got to be a little tougher. So you can see six samples on the slide here. These are all minerals, some more famous than others.
So they all check all the boxes, right? They are naturally occurring inorganic crystalline solids with defined chemical compositions and distinctive physical properties. And yet they look very different from one another.
We can see some key characteristics. For example, this sample here on the far top left is yellow. None of the other samples are yellow.
I'll tell you this because we're doing this virtually. If you come to the City Park campus, I'll let you have a whiff of that. It's going to be very stinky. The center one, we have some shiny examples here.
We can call that metallic because it reflects light. One is silver. One is gold in color. We have pink.
We also have this kind of rectangular shape. Down here, we have kind of a gray, black. sample, but we can also see that staples are sticking to it, suggesting that it is magnetic. We have transparent on the far right, as well as crystalline. So there are several key kind of characteristics or distinctions that we can use to identify minerals.
We're going to define each of those physical properties right now, starting with luster and color. These are going to be two of the most obvious characteristics of a mineral. They're going to be the first thing you notice when you see a mineral on the ground. You're going to say, is it shiny and what color is it?
Luster can be thought of as shiny, not shiny, or metallic, non-metallic. Luster simply represents the intensity of light that can reflect off a mineral surface. So if you were to pick up a metal can without a wrapper, right, you may be able to reflect the light off of the aluminum. It has a metallic luster.
Whereas if you pick up, say, a tissue or a paper towel, it kind of gets illuminated by the light, but it doesn't reflect it in a shiny manner, right? It is non-metallic. So some minerals will have a metallic sheen like the galena here.
Non-metallic is going to be very dull. Doesn't really shine or reflect light easily. Color, we've given two key examples for silicates. Remember, for silicates, we group our silicates into ferro or non-ferro magnesium silicates.
So is there iron? Is there magnesium or not? Depending on the composition of these silicates, we will see a difference in color. We also see color differences in non-silicates as well. Sulfur was an example on the previous slide that was yellow.
But for this class, again, we're really focusing on the silicate side of things. So before we even touch our mineral, right, before we even pick it up off the ground, these are some things we can note, some characteristics we can jot down in our field notebook to help identify a mineral. Next will be crystal form.
Now earlier in this lecture I talked about the crystal structure. We saw cubic versus prism, diamond shaped. Crystal form is how these kind of shapes take hold. We can group or identify minerals based on the number of sides that a crystal form takes. But we have to be careful because different minerals can have the same form.
Now for pyrite or fool's gold on the far left there, it's got a pretty metallic luster. It's pretty distinct. We probably don't have to worry about confusing that specific cubic crystal form with something like fluorite or halite.
But you can imagine if we just had this piece and this piece of fluorite and halite, it might be harder to tell apart. These different minerals do have the same form, so we might need to use other characteristics to help distinguish them. And one way we can do that, do not do what I'm suggesting without the supervision of a proper geologist, is you can lick the halite. It will be salty in taste. But again, do not do that.
Do not go around licking minerals or rocks without the express supervision of a geologist. Because you don't know who's been licking it before. Yucky. After we kind of examine our mineral and take down some notes on what it looks like, now we're going to talk about what physical properties we can use or describe if we actually pick up our mineral. The first two we're going to look at is how a mineral breaks, how it breaks apart.
The first is called cleavage. Minerals naturally break along planes of, that should be planes. sorry, planes of weaker chemical bonds. I will fix that, um, on a canvas.
Sorry, just making a note for myself to get it fixed for y'all. As that breakage occurs, there are strong chemical bonds and weak chemical bonds. The stronger the bonds, the more tightly they're going to hold together. But if things are weak, they're just going to naturally break apart.
So when we have these weak bonds, the mineral will essentially break along these planes or directions. Most simply, we have one directional cleavage plane where it breaks kind of flat, almost like picking up sheets of paper that were stacked together. So there are weak bonds in between each sheet of paper, allowing the material to break apart.
So this is how... minerals will naturally break. Next, we're going to talk about if a geologist has a really, really bad day and they just decide to go off a space or whack a mineral with their rock hammer.
This will cause an irregular breakage called fracture. When we have fracture, we will often see kind of a curved or uneven surface. For fracture, of course, there on the bottom, it's kind of this conchoidal.
kind of circular fracture almost looks like, um, it's hard to see in this image, but it kind of looks like he took an ice cream scoop out of it. This is a regular, so this has nothing necessarily to do with weak bonds. This is everything to do with a large force coming in and just smashing stuff.
So two ways we can break our minerals cleavage, which is the natural. plane, the natural direction by which things want to break or fracture when some sort of external outside force comes in and breaks things irregularly. Another tangible way we can describe our minerals is called hardness. Now, at first you're probably thinking we pick up a mineral and we're just kind of.
hitting it with our hand, kind of, you know, whacking it against our head. Again, do not do that to see how hard it is. And that's not the case.
This hardness is a very, uh, it describes how easily something breaks, but specifically how easily something scratches. This is a minerals resistant to abrasion. Before we even look at the Mohs hardness scale. on the slide here, I'd like to think about diamonds.
Diamonds are incredibly tough or hard minerals. They're used in manufacturing, right? They're very common in jewelry.
They're incredibly difficult to abrade. If you have diamond jewelry, you probably know you can hit it against a wall, a pot, a pan as you're cooking, cleaning, and it's not going to scratch because it's a incredibly resistant to abrasion. Whereas if we had something like talc, which has the consistency of a stick of chalk, we know that we can easily abrade it, right? If I gave you a stick of chalk right now, you'd be able to just scratch it and take clumps out of it. Those are kind of the two most extreme cases of hardness.
Can we scratch it? Yes or no. And so we use the Mohs hardness scale.
to describe how something how resistant something is to abrasion higher values will always scratch lower hardness values. So in the case of a diamond, a diamond will always scratch things like quartz or apatite or calcite, because a diamond is a 10 and a 10 is greater than apatite, which is a five, right? So we can use a diamond to scratch any of those materials. Talc though, because talc is at a one, cannot scratch any of these materials. It is the lowest hardness scale and so everything above it will just break it apart.
And we can use common objects to help determine the hardness of the mineral in the field. Many times geologists will take a number of these small items with them because we can use them to determine the hardness on the go. Something like a fingernail, which can, again, scratch a stick of chalk, a penny. Most of us carry either like a pocket knife when you're in the field or a steel nail. All of these objects, we use them to see if we can scratch a mineral.
And from that, we can determine our hardness value. Another physical property is the density. This is going to be an experimentally determined value, and it is the mass per unit volume. The key thing to take away from this is that metallic minerals, things like, excuse me, ferromagnesian silicates, for example, are going to be denser than non-metallic or non-ferromagnesian silicates. So the more metallic...
dark colored materials are 10, uh, tend to have those heavier or denser properties. And so our darker colored minerals in general will be denser. So metallic will always be denser than non-metallic. There are a number of other properties as well. Um, what, what it feels like there are some minerals that are very, uh, waxy almost.
Um, taste, as I mentioned, do not go around tasting minerals, but we can use it because some minerals will have a salty taste. Give it a lick. Magnetic properties.
We see a sample of magnetite here on the bottom, right? Geologists aren't exactly known for their creativity in naming sometimes, but the name gets the job done. It's states what the mineral is.
Um, streak is if we rub. our mineral on a ceramic plate or a sheet of paper. A famous example of streak is graphite in a pencil.
We use that streak to take notes in our notebook. And then reaction to acid. This is the key reason why we don't want to go around licking minerals unsupervised.
Because if you're in a geology lab, often acid is used to help determine different minerals. So if somebody used acetone on a mineral yesterday, you wouldn't want to be looking at today. Something that we're not going to use to describe the physical properties of a mineral is size.
There can be incredibly large minerals, incredibly small minerals. We will see as we get into chapter four, that size plays a big role for igneous rocks. That's not going to matter here. We're going to use our senses, right?
The sense of touch. the sense of taste, again, only with supervision, what it looks like, sight, to determine what our minerals are. And as we move through the next few chapters, we will talk about how minerals can come together to form rocks. Rocks, by definition, are composed of one or more mineral, and our rocks are grouped or defined based on how they form.
An example would be igneous rocks. Igneous rocks are formed by volcanic processes. So any rock that is formed due to volcanic activity is an igneous rock. That's how we define them. In igneous activities, in volcanic activities, we can have these minerals come together as is the case with granite.
kind of solidifying into a much larger rock. So again, over here we have the ingredients to our recipe and the granite is the outcome. or the soup was an example I gave earlier.
Because most rocks are made up of minerals, or excuse me, rocks are made up of minerals, most of those rocks are going to contain silicate minerals. Because again, our most common elements are silica and oxygen. So those silica and oxygen atoms are going to form our most common bonds, then our most common minerals, then our most common rocks.
And the reason we have to talk about this and have our chemistry review is that when we get to chapter four and chapter five in this exam module, we will see that the silica content, how much silica is present in a material. That's how we classify our igneous rocks, our magma and our lava. Is it silica rich? Is it kind of silica poor?
We use that information. Now, of course, I've mentioned it before. I'll say it again. Mother nature can be quite messy. So even though things like granite, I'm just going to go back for a second.
By definition, we'll have things like feldspar quartz and biotype present. You can see the pink, the black, and the clear components here on the slide. There can occasionally be a sprinkling of other stuff. These are going to be.
present, but small quantities of minerals, just things that find their way into a rock. So they're not going to be a major component, but sometimes they can be found in things like granite. So they're accessories, they're side notes. They're not the main ingredient list.
They're not the primary one. They're just kind of something that's added after the fact. And over the next few chapters, we'll be talking a lot about how minerals form.
In chapters four and five, we will talk about how as magma or lava cools, minerals will start to solidify out from that hot molten material. Then they will crystallize and form larger rocks as well. In chapter six.
We'll talk about how these materials can be broken down or reformed by sedimentary processes on Earth. We know that there is wind, ice, water all across the surface of our planet changing materials. Those minerals can come together to form new rocks, sedimentary rocks.
And then in Chapter 7, we'll talk about how materials on Earth's surface and Earth's interior are subjected to a lot of changes. heat and pressure, as well as chemical reactivity, can cause minerals to break down and reform and eventually form larger rocks that have also undergone significant changes. So that's kind of a roadmap of what's to come. So this is it for our chapter three video lecture. Next up, we're going to jump back to chapter one very briefly to look at learning objective number eight, the rock cycle.
So be sure to check out that video lecture next. It's going to be really, really quick. And then following that, we're going to jump to chapter four. So review these notes.
If you have questions, come to office hours or post them to the discussion board. Get the homework done for chapter three. And then when you're ready to move on. jump to the rock cycle, and then our first rock type igneous rocks. All right, y'all.
See you again soon. Happy studying.