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How to Identify a Mineral. Geology 101: Minerals Part 4 · PlanetGeo: The Geology Podcast

• 0:00
  SPEAKER_01: There we go.
• 0:00
  SPEAKER_01: All right.
• 0:01
  SPEAKER_01: Christopher Bullheis.
• 0:03
  SPEAKER_01: How are you doing, Professor Ramink?
• 0:05
  SPEAKER_01: I'm great, man.
• 0:06
  SPEAKER_01: How are you doing?
• 0:06
  SPEAKER_01: Doing great.
• 0:07
  SPEAKER_01: Doing great.
• 0:07
  SPEAKER_01: You bet.
• 0:08
  SPEAKER_01: I'm ready to go.
• 0:09
  SPEAKER_01: I am too.
• 0:09
  SPEAKER_01: I'm excited.
• 0:10
  SPEAKER_01: Hey, this is wrapping up the minerals chapter.
• 0:12
  SPEAKER_01: This is episode four.
• 0:14
  SPEAKER_01: But before we get into this, I'm going to review what we did last episode.
• 0:17
  SPEAKER_01: Last episode, we talked about the other mineral groups, the other ones apart from the silicates.
• 0:23
  SPEAKER_01: And we also went through the 10 major rock-forming minerals.
• 0:26
  SPEAKER_01: And what we mean by rock forming minerals is the 10 minerals that you are very, very likely to see if you look at a rock.
• 0:34
  SPEAKER_01: And the 10 minerals that, if you know those ones, you can identify most rocks in most minerals that you're going to ever see out there in the world.
• 0:41
  SPEAKER_00: That's right.
• 0:42
  SPEAKER_00: It's like a top 10 list.
• 0:43
  SPEAKER_00: Totally, a top 10 list, exactly.
• 0:45
  SPEAKER_01: And you know, some of our favorites are definitely in there and ones that we do spend a lot of time trying to collect.
• 0:50
  SPEAKER_00: That's right.
• 0:51
  SPEAKER_00: And then today we're going to talk.
• 0:52
  SPEAKER_00: This is our final lecture on the minerals.
• 0:54
  SPEAKER_00: We're going to talk about polymorphs.
• 0:56
  SPEAKER_00: Then we're also going to talk about what the physical properties are of the minerals, like how to identify minerals.
• 1:02
  SPEAKER_00: That's what this is all about.
• 1:04
  SPEAKER_00: So maybe this should have been lecture one.
• 1:07
  SPEAKER_00: I don't know.
• 1:08
  SPEAKER_00: Yeah.
• 1:08
  SPEAKER_01: Well, we're ending this way because, you know, and this is totally in your wheelhouse, the physical properties things, because you have taught a lot of students how to work through this sort of a method to isolate the key mineral properties or the key properties you should use to identify mineral.
• 1:24
  SPEAKER_01: If you're sitting there with an unknown mineral in your hand, whether you're in a lab setting or out there in the world looking at a mineral that you found, you need to work through this flow chart that you've kind of developed.
• 1:34
  SPEAKER_00: Yeah, I think it's bulletproof.
• 1:36
  SPEAKER_00: You know, I think it it's it's of course I developed it, but well, yeah.
• 1:40
  SPEAKER_01: So it's it's obviously great.
• 1:42
  SPEAKER_00: It's just over experience, you know, like over the over the course of my decades-long career.
• 1:48
  SPEAKER_01: Unknown number of decades or an unspecified number of decades.
• 1:51
  SPEAKER_01: That's right.
• 1:52
  SPEAKER_01: But I sound young, right?
• 1:53
  SPEAKER_01: You got a voice for radio, man.
• 1:55
  SPEAKER_01: Um polymorphs.
• 1:57
  SPEAKER_01: So this is uh a term.
• 1:59
  SPEAKER_01: Well, first of all, in your image stack, the first image in the stack is a list of these physical properties that we're going to work through.
• 2:05
  SPEAKER_01: And it sort of goes in this order of an importance of workflow that Chris has really honed in on.
• 2:10
  SPEAKER_01: What we want to start, though, with is a specific definition, which is a polymorph.
• 2:13
  SPEAKER_01: And this is really useful for geologists because it tells us something interesting about where a mineral and therefore the rock that that mineral is in was formed.
• 2:22
  SPEAKER_01: And so, Chris, what is a polymorph?
• 2:24
  SPEAKER_00: Well, you look at the word poly, poly means many, morph means shape or form.
• 2:29
  SPEAKER_00: So, really, what this is are two minerals that have the same chemical composition, but they have different crystalline structures.
• 2:38
  SPEAKER_00: And we talked about this before that, you know, in order for something to be a mineral, it has this definitive crystalline structure.
• 2:44
  SPEAKER_00: So, classic example of polymorphs that you see in any book is going to be graphite and diamond, you know, because they're really, really different like minerals in every way, but they have the same chemical composition.
• 2:59
  SPEAKER_00: They're made of carbon.
• 3:01
  SPEAKER_01: Yeah, and it's extremely valuable for us because we can look at graphite, which is, you know, in your pencils, pencil lead, and that has a very different physical properties than diamond, even though it's still graphite, right?
• 3:12
  SPEAKER_01: I mean, diamonds are beautiful crystallines, they're formed at really high pressure, and the carbon atoms that a diamond is made of are arranged in a different manner that makes them stable at very high pressures and relatively high temperatures compared to graphite.
• 3:25
  SPEAKER_01: So if you just took graphite and heated it up and put it at really high pressure, it would rearrange itself, the carbon would rearrange itself into a more stable configuration that is diamond.
• 3:35
  SPEAKER_00: Right on.
• 3:36
  SPEAKER_00: And you know, you are the expert in the room on this, you're a geochemist.
• 3:41
  SPEAKER_00: So can you like what is what is graphite essentially, and what is diamond, like the internal structure of it, Jess?
• 3:48
  SPEAKER_01: Yeah, so graphite is mainly carbon, and in graphite, each carbon is bonded to three other carbons.
• 3:55
  SPEAKER_01: And so there's a fourth electron that's out there that is weakly shared, right?
• 3:59
  SPEAKER_01: So this makes it a good conductor, but it also means that the bonding environment of that carbon is not as stable as it is in diamond.
• 4:08
  SPEAKER_01: And in diamond, each carbon atom forms a covalent bond with four other carbon atoms.
• 4:13
  SPEAKER_01: So each atom is bonded to four other ones instead of three other ones, and it's a more stable, more densely compacted environment, which is why diamond is more stable at high pressures, because it's a denser configuration of atoms.
• 4:26
  SPEAKER_00: Yeah, that's right.
• 4:27
  SPEAKER_00: And you know, covalent bonds, and you said that all of the carbon atoms are covalently bonded.
• 4:31
  SPEAKER_00: Covalent bonds are the strongest of the chemical bonds.
• 4:34
  SPEAKER_01: Exactly.
• 4:35
  SPEAKER_00: That's the classic example because they're both made of carbon, but they are very, very different minerals because of their internal crystalline structure.
• 4:44
  SPEAKER_00: So, a couple things about this with polymorphs, they've become very good at making synthetic diamonds.
• 4:51
  SPEAKER_00: It's a sophisticated process, you know, because what they do is they'll take like the carbon remains of a pet or a loved one, and they will take those remains and they'll make it into a diamond of your specifications.
• 5:07
  SPEAKER_00: And so I don't know.
• 5:09
  SPEAKER_01: And actually, you know, we've gotten quite good at making synthetic diamonds now in laboratory settings.
• 5:14
  SPEAKER_01: So most of the diamonds you'd find in, you know, diamond sandpaper or anything like that, those are all synthetic diamonds, those are not natural diamonds for the most part.
• 5:20
  SPEAKER_01: And yes, that there's companies that can take your ashes and make a diamond.
• 5:26
  SPEAKER_01: I'm not sure that's so much for me, but you know, whatever.
• 5:28
  SPEAKER_01: Yeah, it's a little weird.
• 5:29
  SPEAKER_01: I know it's a it's cool technology, at least.
• 5:31
  SPEAKER_00: It is one other thing, too, that's interesting to me because I teach astronomy.
• 5:35
  SPEAKER_00: Yeah, until recently, the biggest diamond ever was a little over 3,000 carats.
• 5:40
  SPEAKER_00: Now that's a massive diamond, right?
• 5:43
  SPEAKER_00: Huge.
• 5:43
  SPEAKER_00: Yeah.
• 5:44
  SPEAKER_00: But astronomers have discovered the core, or it's the core of a red giant, actually.
• 5:48
  SPEAKER_00: It's a now a white dwarf.
• 5:50
  SPEAKER_00: So the end, the last stage of life of a star that's like our sun, and that's it's called a white dwarf.
• 5:57
  SPEAKER_00: Anyway, this star stopped fusion and left the core of it as pure carbon.
• 6:02
  SPEAKER_00: So this is a star that is 2,500 miles across that is pure diamond.
• 6:08
  SPEAKER_01: Um super, super dense carbon configuration, which is diamonds.
• 6:13
  SPEAKER_01: Yeah, I mean, totally cool.
• 6:14
  SPEAKER_00: And of course, they named it Lucy after the the Beatles song Lucy and the Sky Diamonds.
• 6:18
  SPEAKER_00: So yeah, that's creative.
• 6:19
  SPEAKER_01: Scientists can be creative in naming.
• 6:21
  SPEAKER_01: All right, Chris.
• 6:22
  SPEAKER_01: So we're gonna come back to polymorphs, especially talk about metamorphic rocks and tectonic study, because it's a useful, really indicator thing.
• 6:28
  SPEAKER_01: So that's why we're kind of talking about it right now and introducing the term in the mineralogy chapter.
• 6:33
  SPEAKER_01: But let's move on to physical properties and work through this kind of flow chart that you've developed.
• 6:38
  SPEAKER_01: So we're gonna start with luster, right?
• 6:41
  SPEAKER_01: But before we get into the physical properties, let's kind of lay the frameworks for why going through this in a very structured manner is important because mineral ID can be incredibly difficult.
• 6:53
  SPEAKER_00: Yeah, it really is.
• 6:54
  SPEAKER_00: And I get it, it's difficult for students.
• 6:56
  SPEAKER_00: And as an instructor, you and I, we both understand this.
• 6:59
  SPEAKER_00: You know, this is difficult for students because this is not two plus two equals four.
• 7:05
  SPEAKER_00: You know, there's some gray area when you're identifying minerals, and you know, students don't like that.
• 7:09
  SPEAKER_00: They want to know.
• 7:10
  SPEAKER_00: You've got a story about this, I think, too, don't you?
• 7:13
  SPEAKER_00: Oh, I absolutely do.
• 7:15
  SPEAKER_00: I mean, you know, when I was in college going through the weeder class was mineralogy, right?
• 7:19
  SPEAKER_00: We had like 300 minerals that we had to identify.
• 7:22
  SPEAKER_00: And on the mineralogy lab exam, that's the man, it's the culminating thing.
• 7:29
  SPEAKER_00: It's the experience.
• 7:30
  SPEAKER_00: So we really had 20 specimens out of that's all the exam was.
• 7:35
  SPEAKER_00: Hey, identify these 20 minerals.
• 7:37
  SPEAKER_00: I look, I'm like, Are you kidding me?
• 7:39
  SPEAKER_00: But look, my prof, he dipped this sample of quartz.
• 7:43
  SPEAKER_00: It was a crystal of quartz.
• 7:44
  SPEAKER_00: He dipped it in graphite.
• 7:46
  SPEAKER_00: And so it has a luster that's different, it has a color that's different.
• 7:49
  SPEAKER_00: It is it's evil, you know, like that is evil.
• 7:52
  SPEAKER_00: Who who does that?
• 7:53
  SPEAKER_00: You know, but the color was wrong, and I could not call the mineral what I knew it was because everything else was right on, but the color was wrong.
• 8:03
  SPEAKER_00: So I got it wrong.
• 8:04
  SPEAKER_00: I got it wrong.
• 8:05
  SPEAKER_01: You know, it's hard even when you're not being tricked by your professor, when you're being tricked by nature.
• 8:10
  SPEAKER_01: I mean, some of the best field geologists that I've ever known, people who mapped rocks for 50 years, they have a hard time identifying minerals.
• 8:17
  SPEAKER_01: And sometimes when you're out in the field, they're just like, I'm not quite sure what this is.
• 8:20
  SPEAKER_01: We got to bring it back to the lab, put it under a microscope, and look at it to really identify it.
• 8:24
  SPEAKER_01: So we're gonna start working through this.
• 8:26
  SPEAKER_00: And in the proxy- Hold on, didn't you have a prof or one of your instructors say to you that we really can't identify minerals in the field that we'd need to actually take it into a lab?
• 8:36
  SPEAKER_01: It wasn't all minerals, like our top 10 list of minerals.
• 8:38
  SPEAKER_01: Most of those you can do a pretty good job of identifying the field, and you should, but there's some weird ones that you definitely won't expect or won't see that you need to bring it back to the lab.
• 8:47
  SPEAKER_01: So, yeah, I've definitely been told this.
• 8:50
  SPEAKER_01: But here's why we got to work through this kind of nice structure.
• 8:53
  SPEAKER_01: We've got to have some structure to interpret these things.
• 8:55
  SPEAKER_01: So, all right, Chris, you got a mineral, you're out on a hike, or you're out in the field, or you're in lab and you've got a mineral, you need to identify what do you start with?
• 9:03
  SPEAKER_01: What's the first physical property?
• 9:05
  SPEAKER_00: Yeah, so the first physical property is luster, which is defined as the way a mineral reflects light.
• 9:11
  SPEAKER_00: Okay, and there are two broad categories of luster.
• 9:13
  SPEAKER_00: There's metallic and there's non-metallic, and it's really self-explaining.
• 9:18
  SPEAKER_00: If it looks like a metal, tastes like a metal, guess what?
• 9:20
  SPEAKER_00: It's a metal, right?
• 9:20
  SPEAKER_00: And so it's a metallic luster.
• 9:22
  SPEAKER_00: And if it's non-metallic, then we have other descriptors for that.
• 9:27
  SPEAKER_00: We call it porcelain-like or vitreous luster, which is really glassy.
• 9:31
  SPEAKER_00: Porcelain is like a dinner plate, I guess, pearly, silky, earthy, all these other descriptors that we use for non-metallic.
• 9:38
  SPEAKER_00: But the point is, is starting with this determines what you do next.
• 9:43
  SPEAKER_00: And this is really important because if you pick up a mineral and it's metallic, then your next test has to be streak.
• 9:53
  SPEAKER_00: To me, that only makes sense.
• 9:55
  SPEAKER_00: And we'll get to that in a minute, what the streak test is.
• 9:57
  SPEAKER_00: But if you pick up a mineral and it's non-metallic, then your next test is not streak because most non-metallic minerals don't give a streak, but the next thing you want to do is a hardness test.
• 10:08
  SPEAKER_01: Yeah.
• 10:09
  SPEAKER_01: So if it's metallic, you could skip ahead to number five on our list.
• 10:12
  SPEAKER_01: If it's non-metallic, we got to go to hardness.
• 10:14
  SPEAKER_01: And Chris, hardness is it's how hard a mineral is.
• 10:18
  SPEAKER_01: And you basically we use a scratch test to determine how hard the thing is.
• 10:22
  SPEAKER_01: You try and scratch the mineral with another object, and then you tell which one scratches which.
• 10:26
  SPEAKER_01: So we always kind of start with the fingernail is kind of an easy one because that's the softest thing you kind of have laying around.
• 10:33
  SPEAKER_00: And we all have one.
• 10:34
  SPEAKER_01: Most people have a fingernail, so you can tell does your fingernail scratch the rock, or does the rock scratch your fingernail?
• 10:40
  SPEAKER_01: But we have this really nice like hardless scale.
• 10:42
  SPEAKER_01: And I always forget these things.
• 10:44
  SPEAKER_01: You have these memorized way better than I than I maybe ever have.
• 10:48
  SPEAKER_01: So take us through the hardness scale.
• 10:49
  SPEAKER_01: What is Mo's hardness scale, which is image two in your stack?
• 10:53
  SPEAKER_00: Yeah, so it's Mo's scale of hardness.
• 10:56
  SPEAKER_00: It's M O H apostrophe S.
• 10:58
  SPEAKER_00: Okay.
• 10:59
  SPEAKER_00: It's basically it's a one through ten.
• 11:01
  SPEAKER_00: Okay, so one is the softest and ten is the hardest.
• 11:04
  SPEAKER_00: So the hardest known substance is diamond.
• 11:06
  SPEAKER_00: Diamond is a 10 out of 10 in a lot of different ways, but including hardness.
• 11:10
  SPEAKER_00: Yes.
• 11:10
  SPEAKER_00: I think it makes sense to start at the soft side.
• 11:13
  SPEAKER_00: So we start with a one, right?
• 11:14
  SPEAKER_00: And so there are different benchmarks that we're gonna put in this scale of one to ten.
• 11:18
  SPEAKER_00: A one is like a bar of soap, super soft.
• 11:21
  SPEAKER_00: Yeah, you can easily scoop into it with your fingernail.
• 11:24
  SPEAKER_00: That's a one.
• 11:25
  SPEAKER_00: Okay.
• 11:26
  SPEAKER_00: So then you go for all right, there's a two, and the next benchmark actually is a two and a half.
• 11:31
  SPEAKER_00: Two and a half is the hardness of a typical fingernail.
• 11:35
  SPEAKER_01: Now I know this isn't like these are all rough numbers for sure.
• 11:39
  SPEAKER_00: There's some grayness, right?
• 11:40
  SPEAKER_00: Absolutely.
• 11:40
  SPEAKER_00: So two and a half.
• 11:41
  SPEAKER_00: So basically, if you can scratch a mineral with your fingernail, it's a two and a half or less, because a two and a half can scratch a two and a half.
• 11:51
  SPEAKER_00: And it's you're assessing how well how easily can I scratch this, right?
• 11:55
  SPEAKER_00: If I can scratch it like a bar of soap, well, that's a one.
• 11:58
  SPEAKER_00: If I can barely scratch it, that's a two, right?
• 12:01
  SPEAKER_00: You know, so you just you're working your way through this.
• 12:03
  SPEAKER_00: Okay, so you pick it up, you scratch your fingernail.
• 12:05
  SPEAKER_00: Nope, can't do it.
• 12:06
  SPEAKER_00: You move on to the next thing.
• 12:08
  SPEAKER_00: And the next thing that we have is a three and a half.
• 12:10
  SPEAKER_00: And what's a three and a half?
• 12:12
  SPEAKER_00: A three and a half on a scale of one to ten is copper.
• 12:15
  SPEAKER_01: So a penny, got a copper penny hanging around.
• 12:18
  SPEAKER_00: Yeah, right on all pennies are at least coated in copper, right?
• 12:23
  SPEAKER_00: So if you can scratch a mineral with a penny, then it's softer than three and a half.
• 12:30
  SPEAKER_00: So you're bracketing it, right?
• 12:32
  SPEAKER_00: Because you couldn't scratch it with your fingernail.
• 12:34
  SPEAKER_00: I can scratch it with a piece of copper that I know is a three and a half.
• 12:38
  SPEAKER_00: So I'm bracketing this and saying, well, then my hardness is around a three.
• 12:42
  SPEAKER_00: You know, and so you're coming up with these numbers this way.
• 12:45
  SPEAKER_01: And so then we move up to what five and a half for uh your typical metal.
• 12:50
  SPEAKER_00: Yeah, it's like it's a five.
• 12:51
  SPEAKER_00: All right.
• 12:52
  SPEAKER_00: So like a scissors, they have a hardness of like a five.
• 12:56
  SPEAKER_00: Okay.
• 12:56
  SPEAKER_00: The next thing up is a piece of glass.
• 12:59
  SPEAKER_00: Glass has a hardness of five and a half.
• 13:01
  SPEAKER_00: This is a critical thing because there are a lot of minerals that are between like a five and a six on the hardness scale.
• 13:09
  SPEAKER_00: So being able to differentiate between a five and a five and a half, that's a big deal.
• 13:15
  SPEAKER_01: Okay, so there's a lot of minerals in this interval, like you said.
• 13:18
  SPEAKER_01: So there's really common minerals out there, like we talked about in our last episode, especially feldspar and quartz become very valuable in this part of Moe's hardness scale because feldspar is a hardness of six and quartz has a hardness of seven.
• 13:31
  SPEAKER_01: And so those two minerals, usually you can find them.
• 13:35
  SPEAKER_01: And if you can identify one of those minerals, then you have a six, a known six, and a known seven in your hand that you can use to compare to other minerals.
• 13:44
  SPEAKER_01: And so, you know, you can kind of use these things.
• 13:46
  SPEAKER_01: Most people have a knife or a piece of glass, and then if you have these two of quartz or feldspar hanging around, you can use those as well.
• 13:53
  SPEAKER_01: So you kind of work your way up in these numbers, and then once you get to a hardness of seven, not a ton is harder than quartz, except diamond and a few other minerals.
• 14:01
  SPEAKER_01: So if it's harder than quartz, if it scratches quartz, you have a pretty hard mineral in your hand, and you've kind of isolated it down quite a bit.
• 14:09
  SPEAKER_00: Yeah, and you can use these minerals like quartz and feldspar, even if you're in the field, you know, you can if they're so common.
• 14:17
  SPEAKER_01: You can usually find a piece of quartz.
• 14:19
  SPEAKER_01: Absolutely.
• 14:20
  SPEAKER_01: All right, so that's Mo's hardness scale.
• 14:23
  SPEAKER_00: Well, I think this is important that, like, okay, so we have the hardness, that's the physical property.
• 14:29
  SPEAKER_00: But what is it that determines the hardness of a mineral?
• 14:33
  SPEAKER_00: Like, why is quartz a seven and why is a mineral like gypsum a two?
• 14:37
  SPEAKER_01: You know, yeah.
• 14:38
  SPEAKER_01: You know, and this is a great question that really comes down to a key feature of minerals that we've touched on before is it's the chemical bonding.
• 14:45
  SPEAKER_01: You think about what's happening when you scratch something, you are breaking chemical bonds.
• 14:50
  SPEAKER_01: And so if I can scratch my fingernail, I'm breaking the chemical bonds within my fingernail to break my fingernail, and that's really what's happening.
• 14:56
  SPEAKER_01: So hard minerals have very tight, compact, firm bonds.
• 15:02
  SPEAKER_01: And weak minerals have at least one direction that has a weak bonding environment.
• 15:08
  SPEAKER_01: So not every bond is the same strength in every direction in a mineral, and we're gonna touch on that in our next property.
• 15:14
  SPEAKER_01: But hard minerals have strong bonds, weak minerals have weak bonds, is basically the way it goes.
• 15:20
  SPEAKER_01: So, Chris, that leads us kind of really nicely into cleavage, which is our next physical property.
• 15:25
  SPEAKER_01: And we're gonna kind of move more quickly through these next ones because they're kind of simple.
• 15:29
  SPEAKER_01: Cleavage is just the tendency, and this is the source of you know an infinite number of geology puns, the term cleavage, right?
• 15:36
  SPEAKER_01: But cleavage is in our definition, is just the tendency of a mineral to cleave or break along parallel planes.
• 15:44
  SPEAKER_01: And so, Chris, what causes a mineral to break this way?
• 15:47
  SPEAKER_01: And well, let me explain what that is a minute.
• 15:49
  SPEAKER_01: So the way to identify cleavage is basically if you break your mineral, and it you could break a big mineral or break your rock and see minerals.
• 15:55
  SPEAKER_01: If you kind of turn it in your hand, if you spin it around and it flashes light at you, that is one singular flat piece of a mineral that is flashing light, and that's cleavage.
• 16:05
  SPEAKER_01: It's breaking along a flat surface, and that is cleavage.
• 16:08
  SPEAKER_01: You know, it's breaking right along a flat surface.
• 16:10
  SPEAKER_01: So, Chris, what causes minerals to behave this way?
• 16:13
  SPEAKER_00: Well, it goes back to what we said earlier that minerals they stack together.
• 16:18
  SPEAKER_00: The way the atoms stack together is consistent, it's always the same.
• 16:22
  SPEAKER_00: There's one best way to put it together.
• 16:24
  SPEAKER_00: Nature finds that way, and that's what you get.
• 16:26
  SPEAKER_00: But like you just said, you have bonds in different directions that are different strengths.
• 16:34
  SPEAKER_00: The analogy that I always use is a chain is only as strong as what?
• 16:40
  SPEAKER_01: It's weakest link, baby.
• 16:41
  SPEAKER_01: It's weakest link.
• 16:42
  SPEAKER_00: That's right.
• 16:43
  SPEAKER_00: So if you stretch a chain that has one weak link, it's always gonna break there, right?
• 16:49
  SPEAKER_00: And so when you break a mineral and it has these, you know, strong bonds and weak bonds that are always in the same direction, it's perfectly consistent, then it's gonna break there all the time.
• 17:01
  SPEAKER_00: Because that's the link in the chain, you know.
• 17:03
  SPEAKER_00: So that's what cleavage is.
• 17:05
  SPEAKER_00: And like you said too, that's a really good point.
• 17:08
  SPEAKER_00: These are hands-on observations and physical tests that we're doing.
• 17:12
  SPEAKER_00: These minerals need to be in your hand, manipulating them, moving them around, and you're looking for flashes of light that are hitting a flat surface as you roll this thing around off a broken surface.
• 17:26
  SPEAKER_00: So that's critical with cleavage.
• 17:29
  SPEAKER_01: And one common mineral that has cleavage, and it's this cleavage is very useful from this is feldspar.
• 17:34
  SPEAKER_01: Feldspar cleaves.
• 17:35
  SPEAKER_01: Feldspar will break along flat surfaces.
• 17:38
  SPEAKER_01: Now, a mineral that is commonly confused with feldspar out there in the world is quartz.
• 17:43
  SPEAKER_01: And quartz does not cleave, it has our next physical property, which is fracture.
• 17:48
  SPEAKER_01: So quartz does not break along flat surfaces, it breaks along an irregular, rough, jagged surface.
• 17:56
  SPEAKER_01: And this is the key thing to distinguishing quartz and feldspar in the field is does it cleave or does it fracture?
• 18:03
  SPEAKER_01: And so, Chris, do you have a good like, you know, uh example of fracture?
• 18:06
  SPEAKER_01: I mean, I always explain it as sort of the light rolls across it.
• 18:09
  SPEAKER_01: You know, if you break your mineral, the light kind of rolls across it.
• 18:13
  SPEAKER_00: It's exactly right.
• 18:14
  SPEAKER_00: When you roll the mineral around underneath light, the light is gonna roll across the surface.
• 18:19
  SPEAKER_00: It's still gonna be shiny, but it's not gonna hit it all at the same time.
• 18:24
  SPEAKER_00: But I think of like when I describe fracture, I think of thick, broken glass.
• 18:30
  SPEAKER_01: Oh, that's a good one.
• 18:31
  SPEAKER_00: And you get this kind of curved break on it, you know, comes to really sharp edges that you can easily cut yourself on and so on.
• 18:38
  SPEAKER_00: Well, this is the same thing that you get with minerals that fracture, it's a curved break, usually, and it comes to sharp, jagged edges.
• 18:46
  SPEAKER_00: That's usually how I think of fracture and how I describe it.
• 18:50
  SPEAKER_00: Obsidian does the same thing, right?
• 18:51
  SPEAKER_00: Obsidian is volcanic glass, but it has that same kind of concoital curved kind of break to it.
• 18:59
  SPEAKER_01: Yeah, that's a great one, Chris.
• 19:01
  SPEAKER_01: Absolutely great one.
• 19:02
  SPEAKER_01: Okay, so we've hit fracture now, and we're gonna be.
• 19:04
  SPEAKER_00: Well, hold on.
• 19:05
  SPEAKER_00: So we need to also, though, we talked about why minerals cleave.
• 19:09
  SPEAKER_00: Why do minerals fracture?
• 19:11
  SPEAKER_01: Well, it's just they don't have a weak plane, they don't have a weak link in their chain.
• 19:16
  SPEAKER_01: And so think of quartz again and go back to our description of bonding environments and silica tetrahedrons.
• 19:21
  SPEAKER_01: Quartz has this interconnected network of silica tetrahedrons that are all bonded together.
• 19:27
  SPEAKER_01: That's a symmetrical bonding environment.
• 19:29
  SPEAKER_01: There is no weak link and no weak plane in there.
• 19:32
  SPEAKER_01: Feldspar, although it is a framework silicate, has a weak plane of bonds in there.
• 19:36
  SPEAKER_01: It has other elements in messing up the silica tetrahedron network.
• 19:40
  SPEAKER_01: So quartz doesn't have a weak link and it doesn't have a weak plane, so it fractures in random.
• 19:45
  SPEAKER_01: It's breaking along random surfaces.
• 19:48
  SPEAKER_00: Exactly.
• 19:49
  SPEAKER_00: This is uh stretching a chain that has all the same strength lengths in it, chain's gonna break, okay?
• 19:56
  SPEAKER_00: But you don't know where it's gonna break, and that's exactly what you get with fracture.
• 20:00
  SPEAKER_01: All right, Chris.
• 20:01
  SPEAKER_01: So number five, streak.
• 20:03
  SPEAKER_01: This is where if you found something metallic right away with a metallic luster, the first thing you would have jumped right to streak.
• 20:09
  SPEAKER_01: So this is useful for metallic minerals, not super useful for non-metallic minerals, but this is a simple one.
• 20:15
  SPEAKER_01: This is just the color of a mineral's powder.
• 20:18
  SPEAKER_01: And this is always a shocking thing.
• 20:20
  SPEAKER_01: I mean, it's still kind of shocking to me that metallic minerals have a different color when they're powdered than when they're not powdered.
• 20:26
  SPEAKER_01: But basically, all you do is you take a mineral and you scratch it along what we call a streak plate or just you know a ceramic.
• 20:33
  SPEAKER_01: Yeah, it's a piece of porcelain.
• 20:34
  SPEAKER_01: Yeah.
• 20:34
  SPEAKER_01: A piece of porcelain, ceramic, and you see what color that streak is.
• 20:37
  SPEAKER_01: And image four in the stack is an image of a mineral that has a different color streak than it does the actual mineral.
• 20:44
  SPEAKER_00: That's right.
• 20:44
  SPEAKER_00: And the best example of this is a metallic mineral called hematite.
• 20:48
  SPEAKER_00: The kind of hematite we get in Michigan and the upper peninsula is this gorgeous, like specular hematite, right?
• 20:54
  SPEAKER_00: It's a beautiful, shiny metallic mineral.
• 20:56
  SPEAKER_00: You streak it on a porcelain plate like this, and the streak is like this reddish brown color.
• 21:01
  SPEAKER_00: When you come across that, you're done.
• 21:04
  SPEAKER_00: You don't need to do anything else.
• 21:06
  SPEAKER_00: You have the mineral hematite, it's a dead giveaway, which is why I tell my students, and for anybody in the field, if you have this, like if you're gonna be identifying minerals and you got a streak plate, metallic minerals, that's the first thing that you want to do after you've identified the metallic luster as a streak.
• 21:22
  SPEAKER_01: So yeah.
• 21:23
  SPEAKER_01: Next one, Chris, is specific gravity, which is basically the density.
• 21:28
  SPEAKER_01: It's the ratio of its weight, of a mineral's weight to an equal volume of water.
• 21:31
  SPEAKER_01: It's a close relative to density.
• 21:33
  SPEAKER_01: So minerals have their own specific gravity, their own density, and that's just a unique identifying property.
• 21:39
  SPEAKER_01: This one's hard to measure unless you're in the lab with a you know quick tool to measure it.
• 21:44
  SPEAKER_01: You can kind of do a rough, is it heavy or is it light kind of test in the field, but you the old half test.
• 21:50
  SPEAKER_01: Yeah, you gotta have a pretty practiced hand to figure that out.
• 21:53
  SPEAKER_01: But it it'll work, you know, as you gain experience, you can use specific gravity a little bit more.
• 21:58
  SPEAKER_00: I will say this though, that in The lab, it's an extremely reliable test.
• 22:04
  SPEAKER_00: This one is more two plus two equals four.
• 22:07
  SPEAKER_01: Yeah, definitely.
• 22:08
  SPEAKER_01: And actually, we use specific gravity to separate minerals from others.
• 22:12
  SPEAKER_01: In our lab, we're interested in separating like diamonds or zircon, which is really dense mineral.
• 22:17
  SPEAKER_01: So we can use this property to separate zircons from all the other minerals in a rock when we're crushing it up and trying to get these out.
• 22:23
  SPEAKER_01: So it's very useful in the lab.
• 22:25
  SPEAKER_01: One that's not super useful, Chris, is color.
• 22:28
  SPEAKER_00: Don't you have this issue with the colors of quartz?
• 22:31
  SPEAKER_00: The different colors of quartz.
• 22:33
  SPEAKER_01: Yeah, I mean, okay, so quartz is a great we use quartz a lot, but this is a great example, right?
• 22:37
  SPEAKER_01: Like a lot of people are familiar with amethyst quartz, the purple one, or rose quartz, the pink one.
• 22:42
  SPEAKER_01: It's all quartz, but it looks so different, right?
• 22:45
  SPEAKER_01: I mean, it's if you saw this pink mineral, this hunk of pink mineral, you would have no idea what it is compared to the purple one.
• 22:51
  SPEAKER_01: You'd think it's something completely different.
• 22:53
  SPEAKER_01: But color can be very misleading because it's all quartz, it just has tiny amounts of impurities in it.
• 23:01
  SPEAKER_01: And so amethyst quartz has uh traces of iron in it, whereas milky quartz can have you know fluid inclusions, so little tiny bits of fluid or gas trapped in them.
• 23:14
  SPEAKER_01: And rose quartz has like phosphate or aluminum.
• 23:18
  SPEAKER_01: Some different colors of quartz have little bits of titanium in them, and then you can have all these mixtures together.
• 23:22
  SPEAKER_01: It could be very confusing using the color to identify a mineral.
• 23:26
  SPEAKER_00: Yeah, Jesse, you and I have gone on many quests for rose quartz.
• 23:32
  SPEAKER_01: Rose quartz is awesome.
• 23:34
  SPEAKER_01: It's so cool.
• 23:35
  SPEAKER_01: Oh man.
• 23:36
  SPEAKER_01: You know, we found some good ones, but I could I still want some more.
• 23:40
  SPEAKER_01: I I have not found my lifetime's supply of rose quartz, I don't think, yet.
• 23:44
  SPEAKER_00: Do you remember laughing your ass off at me when I'm standing in this mine hang?
• 23:49
  SPEAKER_00: I'm I have this massive quartz specimen in my hand, and you guys thought it was the biggest piece of shit ever.
• 23:56
  SPEAKER_01: You remember that?
• 23:56
  SPEAKER_01: You must have thrown that away because that was not a very good piece, but you I don't I still have it.
• 24:01
  SPEAKER_00: I actually love this, I love the sample.
• 24:03
  SPEAKER_00: I think you guys are crazy.
• 24:04
  SPEAKER_00: I love it.
• 24:05
  SPEAKER_00: You were risking life and limbs.
• 24:06
  SPEAKER_01: No, no, let me tell you you were risking life and limbs stumbling down this scree slope.
• 24:11
  SPEAKER_01: You were so proud of this thing, and we're like, Chris, you're gonna break your leg and we're gonna have to haul your ass out of here.
• 24:16
  SPEAKER_01: Uh, all for some beautiful rose quartz.
• 24:19
  SPEAKER_00: I love it though, because it's all milky on one side, and then this corner of the sample is all like bright, bright pink.
• 24:26
  SPEAKER_00: It's beautiful.
• 24:27
  SPEAKER_00: You guys were wrong, I was right.
• 24:29
  SPEAKER_00: Okay, all right.
• 24:30
  SPEAKER_00: So anyway, okay.
• 24:31
  SPEAKER_00: All right, so that's color.
• 24:32
  SPEAKER_00: Yeah, the next one is uh crystal form.
• 24:34
  SPEAKER_00: We touched on this earlier, the way the minerals stack together, right?
• 24:37
  SPEAKER_00: Crystal form is consistent.
• 24:39
  SPEAKER_00: Again, coming back to quartz.
• 24:42
  SPEAKER_00: The best way to stack silicon dioxide together is to make hexagonal crystal forms, you know.
• 24:49
  SPEAKER_00: That's so if you're fortunate enough to have room where the crystal grew unimpeded, then quartz is always going to be hexagonal because that's the best way to stack it together.
• 24:59
  SPEAKER_00: So crystal form can be reliable.
• 25:01
  SPEAKER_01: Yeah, and you just really nailed it with the the last comment there is if you have enough room for a crystal to grow, it is completely diagnostic.
• 25:09
  SPEAKER_01: If you have a beautiful crystal, it's diagnostic of that mineral.
• 25:12
  SPEAKER_01: But usually in geology out there in the real world, crystals do not have enough space to grow into their true crystal form.
• 25:19
  SPEAKER_01: So we get crystals that don't that just kind of fill in space.
• 25:23
  SPEAKER_01: Yeah, they grow into each other.
• 25:24
  SPEAKER_01: Yeah, we can't really use crystal form as much as we would like to, and that's why it's low down in the list of these physical properties.
• 25:32
  SPEAKER_00: However, professors like you love, love to throw crystals on exams, which is like tricky was on an understanding.
• 25:42
  SPEAKER_01: Yeah.
• 25:42
  SPEAKER_01: Our fifth image in your stack is a picture of a beautiful mineral with a beautiful crystal form.
• 25:48
  SPEAKER_01: And if again, if you see this, it's diagnostic of that type of mineral.
• 25:52
  SPEAKER_01: All right, Chris, there's a few more properties that we just kind of have to touch on because they're really specific to certain minerals like magnetism.
• 25:59
  SPEAKER_01: If you find a mineral that's magnetic, and a lot of us who go out in the field and try and identify minerals will carry around a little tool that has a little magnet on it, just so we can test if the mineral is magnetic or not.
• 26:08
  SPEAKER_01: Because if it's magnetic, it's almost assuredly magnetite, the mineral.
• 26:12
  SPEAKER_01: There are other ones like fluorescence though or translucency.
• 26:16
  SPEAKER_01: And uh the last image in your stack is a fluorescent mineral, which if it shines under UV light, it fluoresces.
• 26:23
  SPEAKER_00: Yeah, that's actually the mineral Willamite from New Jersey, just absolutely beautiful under the black light.
• 26:29
  SPEAKER_00: So, yeah, totally beautiful.
• 26:31
  SPEAKER_01: All right, Chris, are you ready for a couple questions, real quick?
• 26:35
  SPEAKER_01: That's my favorite part.
• 26:36
  SPEAKER_01: Let's go.
• 26:37
  SPEAKER_01: Your face just lit up.
• 26:38
  SPEAKER_01: I love it.
• 26:38
  SPEAKER_01: Okay.
• 26:39
  SPEAKER_01: So these are, you know, I've been a little bit hard on you, so these are a little bit easier.
• 26:42
  SPEAKER_01: Oh, really?
• 26:43
  SPEAKER_01: So, you know, you can relax a little bit.
• 26:45
  SPEAKER_01: So the first one, what is the most reliable physical property to use to identify a mineral?
• 26:51
  SPEAKER_01: The most reliable.
• 26:52
  SPEAKER_01: Is it a luster, B, the combination of cleavage or fracture, or C, the combination of many of them?
• 27:01
  SPEAKER_00: Yeah, so actually, I answered the question before you started giving me the choices, and I'm like, well, wait a minute, that's a very misleading question.
• 27:09
  SPEAKER_00: But your last choice brought it all together.
• 27:12
  SPEAKER_00: It's C, clearly.
• 27:13
  SPEAKER_01: All of them.
• 27:14
  SPEAKER_01: It's a combination, all of them.
• 27:16
  SPEAKER_01: Lusters where we start, and cleavage and fracture are very useful for some key ones.
• 27:20
  SPEAKER_01: Feldzbar quartz, totally useful.
• 27:22
  SPEAKER_00: Cleavage and fracture can be very difficult too for beginning students to identify does this mineral cleave or does it fracture?
• 27:29
  SPEAKER_00: Yeah, but it's really, really useful.
• 27:31
  SPEAKER_01: Okay, you ready for the uh opposite question?
• 27:34
  SPEAKER_01: What is the least reliable physical property?
• 27:36
  SPEAKER_01: Is it a crystal form?
• 27:38
  SPEAKER_01: B color or C There we go.
• 27:41
  SPEAKER_00: Color.
• 27:42
  SPEAKER_00: Color.
• 27:43
  SPEAKER_00: Good.
• 27:43
  SPEAKER_00: Well, unless you're dealing with minerals like biotite or sulfur, things like that, or malachite, you know, minerals that like they're these bam, that's the color of that mineral in your dawn.
• 27:56
  SPEAKER_00: It's just uh, but with the most common minerals in the world, doesn't work that way.
• 28:01
  SPEAKER_01: Yeah, that's right.
• 28:01
  SPEAKER_01: They have lots of flavors.
• 28:03
  SPEAKER_01: I just want to end with one thing here is that as we work forward through these chapters, mineral associations become really important.
• 28:10
  SPEAKER_01: So if you see biotite in your rock, you might think, oh, there might be quartz around here, or there might be feldspars.
• 28:15
  SPEAKER_01: So as we work through rocks in the next couple chapters, the associations of the minerals become really important.
• 28:20
  SPEAKER_01: And that's where we're going next, Chris, is the next chapter, sedimentary rocks, really exciting stuff.
• 28:26
  SPEAKER_01: And you know, sedimentary rocks are awesome.
• 28:28
  SPEAKER_01: We've we've seen a lot of them together.
• 28:30
  SPEAKER_00: They just might be the most important rock on the planet.
• 28:34
  SPEAKER_01: Ah, I hate to admit that.
• 28:36
  SPEAKER_01: As somebody who studies igneous rocks for a living, I hate to admit that, but it might be true.
• 28:41
  SPEAKER_01: It might be.
• 28:42
  SPEAKER_01: It might be.
• 28:43
  SPEAKER_01: That's a wrap on minerals.
• 28:44
  SPEAKER_01: Good stuff.
• 28:45
  SPEAKER_01: That's right.
• 28:46
  SPEAKER_01: See ya next unit.
• 28:48
  SPEAKER_00: All right.