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How to Identify Rocks - Rerelease · PlanetGeo: The Geology Podcast

• 0:02
  SPEAKER_00: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
• 0:13
  SPEAKER_00: Today we have part three of our holiday re-release series where we are revisiting some of our favorite episodes about rock identification and collecting.
• 0:20
  SPEAKER_00: Today's episode is a bit of an intro into the strategies and just general methods that you should think about when you see an interesting rock out there in the wild.
• 0:28
  SPEAKER_00: We, as Chris and I, we get this question a lot: how do you identify rocks?
• 0:32
  SPEAKER_00: And this is just a general strategy and overview.
• 0:34
  SPEAKER_00: So if you like getting outside and learning, maybe you're a biting rock hound, this episode is for you.
• 0:38
  SPEAKER_00: Coming up in a few weeks, we'll begin launching new episodes with, as I've said before, a slightly modified version of Planet Geo to launch year six, which is kind of crazy to say, of the Planet Geo podcast.
• 0:48
  SPEAKER_00: We will have deep dive question and answer episodes with Dr.
• 0:51
  SPEAKER_00: Rachel Phillips.
• 0:52
  SPEAKER_00: So you can message her on our YouTube channel at Geogirl or shoot us an email via the contact us link on our website, Planetgeocast.com.
• 0:59
  SPEAKER_00: We will also have a current geology news series and some geochronology deep dives with my good buddy Dr.
• 1:05
  SPEAKER_00: Josh Davies.
• 1:06
  SPEAKER_00: We'll have interviews with top geoscientists, and of course, Chris will continue to be involved in many of these episodes too.
• 1:11
  SPEAKER_00: So if you're missing you some Chris, I know that I am.
• 1:13
  SPEAKER_00: Never fear, he's still going to be around regularly.
• 1:16
  SPEAKER_00: Lastly, you can follow us on all the social medias, playing a geocast, download our Camp Geo mobile app.
• 1:21
  SPEAKER_00: First link in your show notes.
• 1:22
  SPEAKER_00: There's tons of free content there, in addition to some very cool visual podcast series, and we will have some really exciting new content coming to that app in 2026.
• 1:30
  SPEAKER_00: So stay tuned on that front.
• 1:32
  SPEAKER_00: Okay, let's talk about rock identification.
• 1:36
  SPEAKER_00: Today's episode, Chris, is we could spend six hours talking about this.
• 1:41
  SPEAKER_00: So we're gonna have to rein each other in, I think, on this topic because it's a deep one.
• 1:47
  SPEAKER_00: And it's basically inspired by listener question.
• 1:50
  SPEAKER_00: And many people have this question, and we've gotten kind of similar, vaguely similar questions from a lot of people.
• 1:55
  SPEAKER_00: And the summary is how do you identify rocks?
• 1:57
  SPEAKER_00: Like what are some key guidelines to identifying rocks when you're not a rock identification expert, right?
• 2:04
  SPEAKER_00: You're not a field geologist.
• 2:05
  SPEAKER_01: You are instead going to be Is there such a thing as a rock identifying expert?
• 2:10
  SPEAKER_00: Well, Chris, just ask me.
• 2:12
  SPEAKER_00: I think I'm no, I'm kidding.
• 2:14
  SPEAKER_00: Um no, not at all.
• 2:15
  SPEAKER_00: Uh but the the quite okay, you're out there going on a hike, you're hiking to, in this case, you know, Richard was talking about old mine sites, or you're just out there hiking along a beautiful path, and there's rocks around, and there's you're trying to look at the rocks and understand what they were.
• 2:28
  SPEAKER_00: You're trying to extract the story of the rocks.
• 2:30
  SPEAKER_00: Like, how do you go about that?
• 2:32
  SPEAKER_00: This is a really interesting and deep question.
• 2:35
  SPEAKER_01: Yes.
• 2:35
  SPEAKER_01: So are you asking me how I go about this?
• 2:37
  SPEAKER_01: Is that what you just did?
• 2:38
  SPEAKER_01: Did you flip me the question?
• 2:40
  SPEAKER_00: No, I don't think so.
• 2:40
  SPEAKER_00: I'm asking what do you think about the question, I suppose, and then how are we gonna even start to approach it?
• 2:45
  SPEAKER_00: Because it's such a big topic.
• 2:46
  SPEAKER_01: Yeah, it is a huge topic, and it's a it can be really difficult because there are so many nuances in geology and rock identification.
• 2:56
  SPEAKER_01: There I try to keep it really simple.
• 2:58
  SPEAKER_01: If you pick something up, a rock in the field that is outside of this idealistic system that I'm gonna go through, like the what is it, 25 maybe rocks that I have my kids identify in my class, and you probably have maybe a little less.
• 3:12
  SPEAKER_01: Like you probably don't have your students identify that many rocks.
• 3:16
  SPEAKER_00: Yeah, is that right?
• 3:17
  SPEAKER_00: We don't, I mean, we don't have a final exam identification, we don't have a lab final exam like you do.
• 3:22
  SPEAKER_00: So we basically have a bunch of rocks they identify during labs, but then it's not like a holistic thing that they have to know these 25 or something like that.
• 3:30
  SPEAKER_00: So they see a lot more, but they don't have to know them all, like they have to know it for one lab session, and that's it.
• 3:35
  SPEAKER_01: Gotcha.
• 3:36
  SPEAKER_01: Yeah, so my point is that you're gonna pick things up that are outside of that system, and you have to just take a piece of it home or take a picture of it, and then when you get back home or you get back to where you, you know, where you come from, then you start looking it up.
• 3:51
  SPEAKER_01: What's the geology of the area where you were?
• 3:54
  SPEAKER_01: And you're gonna have success then I think finding out exactly what's in your hand.
• 3:58
  SPEAKER_01: Because chances are somebody's done research on this, especially if it's like a mine or a rather well-traveled place.
• 4:04
  SPEAKER_00: Yeah, uh so there's a couple ways that my mind goes here, and a couple things that we could use to structure this episode.
• 4:11
  SPEAKER_00: The first is resources, like what resources should we point people to that can help them start down this path?
• 4:16
  SPEAKER_00: We should definitely touch on that.
• 4:18
  SPEAKER_00: We should talk about like what happens, what do we do?
• 4:20
  SPEAKER_00: What do you and I do when we come across an unknown rock in the field?
• 4:23
  SPEAKER_00: Like, how do we mentally work through that?
• 4:25
  SPEAKER_00: And then also talk about what are the things you should know while you're out there?
• 4:29
  SPEAKER_00: Like we cover the 10 rock-forming minerals in Camp Geo, right?
• 4:34
  SPEAKER_00: The first link in your show notes, you can go there and learn about these minerals.
• 4:37
  SPEAKER_00: What are things like that that people should absolutely know while they're out there in the field before they take a picture and take a little piece of the rock home if they want and try and identify it, right?
• 4:46
  SPEAKER_00: Like what are the does that make sense?
• 4:48
  SPEAKER_00: Like there's skill sets, there's the way your mind works, and then there's the resources to use.
• 4:52
  SPEAKER_00: I don't know.
• 4:53
  SPEAKER_00: What do you think about that?
• 4:54
  SPEAKER_01: My mind just went in a thousand different directions all at once, right there.
• 4:58
  SPEAKER_01: There's so much going on in my head.
• 5:00
  SPEAKER_01: I think great resources.
• 5:02
  SPEAKER_01: Let's start with that.
• 5:03
  SPEAKER_01: I think the roadside geology series are awesome because it's so well organized.
• 5:09
  SPEAKER_01: It gives you the geology according to where you are in that particular state.
• 5:14
  SPEAKER_01: It's organized by states usually.
• 5:16
  SPEAKER_01: Sometimes it's organized by where you are inside of a very well-known national park, too.
• 5:22
  SPEAKER_01: So they're they're very well organized.
• 5:23
  SPEAKER_01: And then you can, if you pick up a rock, you know, that is near a road, then you can look up that road in the roadside geology series, and it's going to talk to you about that.
• 5:34
  SPEAKER_01: So I think that's a really good resource.
• 5:36
  SPEAKER_01: Or Geology Underfoot is another good series that's organized in a little bit of a different way, but it's indexable, if that makes sense.
• 5:44
  SPEAKER_01: So you you know, you can just look stuff up.
• 5:46
  SPEAKER_01: I think those are two really good resources.
• 5:49
  SPEAKER_01: And then just Google searching, you know, where you are, and I found this really weird rock, and you will be amazed at what people have put out there.
• 5:59
  SPEAKER_00: Yeah, that that's a great point.
• 6:00
  SPEAKER_00: And I think maybe I can summarize the resources.
• 6:02
  SPEAKER_00: You're talking about location-specific resources, and this is a really important point about this.
• 6:07
  SPEAKER_00: Like, you have to know the area you're in, the general geology of the path you're on, the park you're in, the old mine site you're at.
• 6:15
  SPEAKER_00: Like, there are resources online about that.
• 6:17
  SPEAKER_00: There are probably some books written about that as well that give you at least a narrow down your list of options, right?
• 6:23
  SPEAKER_00: When you're looking at a rock, you don't know what it is.
• 6:26
  SPEAKER_00: Knowing something about the region narrows down your list of potential options for this particular rock you're holding in your hand, right?
• 6:33
  SPEAKER_01: That's right.
• 6:34
  SPEAKER_01: And I I think that doing that on the front end of a trip anyway is really, really important because it's gonna allow you the more you know about where you're going, is gonna give you a different lens to view that area.
• 6:46
  SPEAKER_01: Uh just a little bit of knowledge just totally changes your perspective and what you're seeing.
• 6:50
  SPEAKER_00: So Yeah, Chris, and you know what?
• 6:51
  SPEAKER_00: Let me just let me interrupt you there, because we're gonna have a couple episodes on this exact topic, like what we do before we're going on a trip, what we look at, what we learn about while you're planning the trip to really get the full geological experience of that trip.
• 7:05
  SPEAKER_00: So more to come on that front.
• 7:07
  SPEAKER_00: Okay, maybe let's back up and say, well, what do you do, Chris?
• 7:10
  SPEAKER_00: If you come across, I don't know, what if you come across a random rock and let's say I've handed you a rock and said, What is this, Chris?
• 7:18
  SPEAKER_00: Like, where does your mind go?
• 7:19
  SPEAKER_00: How do you work through it?
• 7:20
  SPEAKER_01: I think you and I are gonna answer this question about how we do this, I think in really different ways.
• 7:26
  SPEAKER_01: I'm gonna bring a more simplistic approach, I think.
• 7:28
  SPEAKER_01: Uh, you know, more of a layperson's approach to rock identification than what you're gonna do.
• 7:32
  SPEAKER_00: Uh that's because you learned from the textbooks of the 1960s.
• 7:37
  SPEAKER_00: Um and before in the pre-plectonic pre-pre tectonic era, it things were a lot simpler, right, Chris?
• 7:43
  SPEAKER_00: Hey, yeah, that's right.
• 7:45
  SPEAKER_01: Um so I think, first of all, the what you should have with you, it's helpful when you're gonna identify rocks, or you know, to have a little magnifying lens or a little geologic little hand lens that you can wear as a necklace.
• 7:58
  SPEAKER_01: I think a little bottle of acid is helpful.
• 8:00
  SPEAKER_01: And a hammer is helpful because when you're gonna identify rocks, you want to have a fresh break on that rock.
• 8:09
  SPEAKER_01: I can't tell you the number of times students bring rocks into me that they pick up.
• 8:13
  SPEAKER_01: It happens weekly or not quite daily, but almost, where people are bringing rocks into me and they're like, What is this?
• 8:20
  SPEAKER_01: And some of the times I don't know because I have no context, first of all.
• 8:24
  SPEAKER_01: I don't know where it came from, and it's a weathered surface that I'm looking at.
• 8:28
  SPEAKER_01: So it's got oxidation on it.
• 8:29
  SPEAKER_01: You I can't see the minerals that are inside the rock.
• 8:32
  SPEAKER_01: So I'll ask him, can I break it?
• 8:34
  SPEAKER_01: You know, if I can break it open, I can probably tell you more about what it is.
• 8:38
  SPEAKER_01: So you really do need to have a fresh break, and that's the importance of having a hammer.
• 8:42
  SPEAKER_00: I I think that's a really good point, Chris.
• 8:44
  SPEAKER_00: And you don't need so this goes back to our interview with Andrew Alden about the geology of Oakland, and he brings a rock hammer out, or he used to at least, right?
• 8:52
  SPEAKER_00: He doesn't bash outcrop.
• 8:53
  SPEAKER_00: So two things about that.
• 8:55
  SPEAKER_00: Absolutely, a hammer is a great thing to have.
• 8:56
  SPEAKER_00: You don't need a big heavy hammer, though, like those little pickaxe hammers that we always use, Estwing, uh, the company Estwing, they make great little geological hammers that you just need a little, knock a little corner off.
• 9:08
  SPEAKER_00: But point number two, you have to be extremely selective.
• 9:12
  SPEAKER_00: Do not damage valuable outcrops and be very careful about this because you know it's easy to A, hurt yourself and B, damage valuable sites if you're just bashing rocks, you know, on a whim.
• 9:22
  SPEAKER_00: Indiscriminately.
• 9:23
  SPEAKER_00: Indiscriminately.
• 9:23
  SPEAKER_00: Just be very careful of that.
• 9:25
  SPEAKER_00: But I think you're exactly right, Chris.
• 9:26
  SPEAKER_00: This is a knowing what is alteration or surface weathering and what is internal to the rock is a really uh it takes a lot to know that, to work through that.
• 9:37
  SPEAKER_00: We my wife and I, you know, we have this little Etsy bookshop where we make bookends and things like that.
• 9:41
  SPEAKER_00: And the number of times that we I pick up a rock and I think it's gonna be cool inside, and she's like, no, no, it looks crappy, it's brown, it's outside.
• 9:47
  SPEAKER_00: I'm like, well, I I know that that's weathering.
• 9:50
  SPEAKER_00: Like I can identify what's weathering and what's not weathering, but that's a really hard skill, and it takes a lot of practice to identify that.
• 9:56
  SPEAKER_00: And sometimes you and I don't know if it's weathering or if it's you know, if that weathering is going to be through the rock or if it's not going to be when I cut it open.
• 10:04
  SPEAKER_00: Like it's a really difficult question.
• 10:06
  SPEAKER_01: Or when you step into a river and you see a pretty pebble in the bottom of it and you pick it up, you can't see what's inside of it in that situation.
• 10:13
  SPEAKER_01: And that's usually what is brought into me.
• 10:16
  SPEAKER_01: Little small pieces that people pick up from a river because it's cool looking, and you really have no idea until you break that thing open.
• 10:24
  SPEAKER_01: Um, okay.
• 10:25
  SPEAKER_01: So here's my generalized approach to identifying rocks.
• 10:29
  SPEAKER_01: I have my three things.
• 10:30
  SPEAKER_01: I got my hammer and I have my hand lens.
• 10:33
  SPEAKER_01: So I do it this way.
• 10:35
  SPEAKER_01: I start with the biggest thing in identifying rocks to my students.
• 10:41
  SPEAKER_01: Look, they pick it up and the first thing they try to do is name it.
• 10:44
  SPEAKER_01: And I think that's wrong.
• 10:45
  SPEAKER_01: I think what you should do is pick up a rock and first classify it.
• 10:50
  SPEAKER_01: Are you a sedimentary rock?
• 10:52
  SPEAKER_01: Are you a metamorphic rock, or are you an igneous rock?
• 10:56
  SPEAKER_01: If you can do that, then I think that you're 85% done in identifying that rock.
• 11:02
  SPEAKER_01: I really, really believe that.
• 11:04
  SPEAKER_01: That's something that I've learned over the years.
• 11:06
  SPEAKER_01: That's right.
• 11:06
  SPEAKER_00: Because you've narrowed down the list of potential things that uh that can do that.
• 11:10
  SPEAKER_00: So how do you go about narrowing down that?
• 11:12
  SPEAKER_00: You personally, not your students.
• 11:14
  SPEAKER_00: How do you do it?
• 11:15
  SPEAKER_00: Like, what do you do to narrow that down?
• 11:17
  SPEAKER_01: So if I pick up a rock, I'm looking around the area too.
• 11:20
  SPEAKER_01: Or what what do I see?
• 11:22
  SPEAKER_01: Here's my protocol.
• 11:24
  SPEAKER_01: Are you sedimentary?
• 11:26
  SPEAKER_01: Are you metamorphic?
• 11:28
  SPEAKER_01: And then lastly, okay, you're none of those, then you must be igneous.
• 11:32
  SPEAKER_01: So let's deal with sedimentary.
• 11:33
  SPEAKER_01: What do sedimentary rocks look like?
• 11:35
  SPEAKER_01: Well, if it looks like dirt, tastes like dirt, it's dirt, you know, and it's it we talk about like sedimentary structures.
• 11:42
  SPEAKER_01: You know, does it have any signs of fossils in it?
• 11:44
  SPEAKER_01: Does it have stratification, which is just layering in it?
• 11:48
  SPEAKER_01: Is it kind of weaker and softer?
• 11:51
  SPEAKER_01: So you take a rock and you crack it open, you get a fresh break, right?
• 11:54
  SPEAKER_01: Now you take your hand lens out and you try to look at the way the grains are held together with that magnifying glass.
• 12:02
  SPEAKER_01: Are they interlocking or are they held together by a cementing agent during the lithification of sedimentary rock formation?
• 12:12
  SPEAKER_01: By looking at that at like inside the rock now, just the way the grains are kind of stuck together can be really helpful in terms of okay, if they're not interlocking, that's a really good sign that that's a sedimentary rock that you have in your hand.
• 12:29
  SPEAKER_01: Does that make sense?
• 12:30
  SPEAKER_01: Yeah, yeah, absolutely.
• 12:31
  SPEAKER_01: Like so I do that, and then of course, you know, you have your common sedimentary rocks, right?
• 12:36
  SPEAKER_01: You have conglomerate and brecia, you have your sandstones, you have shale, and you have limestone and dolostone.
• 12:45
  SPEAKER_01: Those are the common sedimentary rocks.
• 12:46
  SPEAKER_01: And if you come up with a sedimentary rock that is outside of that, like settle down, take a little piece of it home, and learn about what that might be based upon what some some other source provided information on that area, then.
• 13:00
  SPEAKER_01: That's what I would do.
• 13:01
  SPEAKER_01: So is it sedimentary?
• 13:04
  SPEAKER_01: Then now I can identify the rock because now I'm I'm sifting through a vocabulary that is a much shorter list.
• 13:10
  SPEAKER_01: I'm looking through five or six names, and there's like a it's an easy process at that point.
• 13:15
  SPEAKER_01: If I can get to this rock is sedimentary, I can identify that rock 98% of the time.
• 13:20
  SPEAKER_00: Okay, Chris.
• 13:21
  SPEAKER_00: So so you you you first tackle, is it sediment, right?
• 13:24
  SPEAKER_00: Are you a sedimentary rock?
• 13:25
  SPEAKER_00: Then you go to metamorphic.
• 13:26
  SPEAKER_00: Is that what you said?
• 13:27
  SPEAKER_00: You kind of move to are you metamorphic?
• 13:28
  SPEAKER_00: And what's uh how do you distinguish between those two, or like what are some keys you're looking for in that next, you know, question one B that you're asking the rock?
• 13:38
  SPEAKER_01: Okay.
• 13:38
  SPEAKER_01: Metamorphic rocks fall into two categories.
• 13:41
  SPEAKER_01: They're either foliated or they're non-foliated.
• 13:44
  SPEAKER_01: And the foliated metamorphic rocks, that just means that the minerals have an alignment, they have some sort of pattern because they were heated and squeezed.
• 13:53
  SPEAKER_01: The heat causes the rock to become soft, the pressure allows the minerals to like reform and align according to that pressure.
• 14:00
  SPEAKER_01: So I'm looking for some sort of visible pattern in a foliated rock.
• 14:05
  SPEAKER_01: And if I see that, and this is not foliation, it's a pattern that's created by pressure, right?
• 14:11
  SPEAKER_01: If I see that, I'm like, you're metamorphic.
• 14:13
  SPEAKER_01: And then the two really common non-foliated metamorphic rocks are quartzite and marble.
• 14:18
  SPEAKER_01: And you kind of need to know the nuances of what quartzite and marble look like.
• 14:22
  SPEAKER_01: You know, marble is a calcium carbonate, so you can put a drop of acid on it and it'll fizz like limestone.
• 14:28
  SPEAKER_01: Quartzite has this kind of chipping or flaky appearance on a broken surface.
• 14:33
  SPEAKER_01: It has these little nuances that will help you, oh, this is non-foliated quartzite or marble.
• 14:38
  SPEAKER_01: So that's what I do there.
• 14:40
  SPEAKER_01: I'm looking for a pattern, or are you quartzite or marble?
• 14:44
  SPEAKER_01: And if I'm like, okay, no, you're not sedimentary, you are not metamorphic, then it has to be an igneous rock.
• 14:51
  SPEAKER_00: Okay.
• 14:51
  SPEAKER_00: And then if you get to that point where it's saying, Oh, okay, you're igneous, I know you're igneous, like, how do you go into that, I guess?
• 14:58
  SPEAKER_00: How do you how do you sort of like how do I go with what am I looking for if it's igneous?
• 15:02
  SPEAKER_00: How do you keep refining if it's an igneous rock?
• 15:05
  SPEAKER_00: You know what I mean?
• 15:05
  SPEAKER_00: If you end at, oh, you're an igneous rock, what's next?
• 15:09
  SPEAKER_01: What color are you?
• 15:10
  SPEAKER_01: You know, are you light colored?
• 15:11
  SPEAKER_01: Yeah.
• 15:12
  SPEAKER_01: Are you know are you light colored?
• 15:14
  SPEAKER_01: Are you dark colored, or are you intermediate colored?
• 15:17
  SPEAKER_01: I I start with that because it's just so easy, and that tells us a broad type of chemical composition of that rock.
• 15:25
  SPEAKER_01: And then I look at the texture of it.
• 15:27
  SPEAKER_01: Are you a fine-grained igneous rock, which means you cooled fast, or are you a coarse-grained igneous rock, which means you cooled slowly, or are you a porphyritic igneous rock, which means you had two different rates of cooling, which is typical in some volcanic settings?
• 15:42
  SPEAKER_01: So that's the way I go through rock identification.
• 15:46
  SPEAKER_00: Yeah, this is an interesting thing, because you know, Chris, you and I have we've identified a lot of rocks together, but it's also been a minute since we've been on one of our camping trips, right?
• 15:56
  SPEAKER_00: Like, you know, I don't know, it's been a decade, if not more, probably, since we've actually done this where we're in a place where neither of us knows what's going on and we're trying to work through this.
• 16:04
  SPEAKER_00: I mean, we've done this a lot before, but we've both had a lot of experiences since that time, right?
• 16:09
  SPEAKER_00: Like since those rock collecting days up in Maine or out in the Black Hills, right?
• 16:14
  SPEAKER_01: It has been a little bit, yeah.
• 16:15
  SPEAKER_01: So is my system too simplistic for you then?
• 16:18
  SPEAKER_01: Like what do you think?
• 16:20
  SPEAKER_00: I don't think it's simplistic, it's different for sure, but I don't think it's too simplistic.
• 16:23
  SPEAKER_00: I think we we definitely have slightly different approaches.
• 16:26
  SPEAKER_00: So I guess it would be fun to go collect rocks or go look at rocks that neither of us know again at some point soon here.
• 16:34
  SPEAKER_00: Because it'd be fun to work through this together.
• 16:35
  SPEAKER_01: That's right, that's right.
• 16:36
  SPEAKER_01: It is, but you know, that doesn't happen very often with you and I because we do our research on the front end.
• 16:42
  SPEAKER_01: You know, we that's true, we do a deep dive before we go, so we have a really good idea of where we're gonna go and what we're gonna find when we get there, and that's so helpful.
• 16:53
  SPEAKER_01: But all right, tell us about your approach then.
• 16:56
  SPEAKER_01: Well, like, or how would you teach other people to do it?
• 16:59
  SPEAKER_00: This was a hard one for me.
• 17:00
  SPEAKER_00: Like when we were we were sort of prepping for this, I I sort of thought, okay, how do I do this?
• 17:05
  SPEAKER_00: Like, it's hard to explain your mental thought process that you go through.
• 17:09
  SPEAKER_00: So, this is a guess.
• 17:10
  SPEAKER_00: This is what I think I do.
• 17:12
  SPEAKER_00: I basically, I think the first thing is I have to figure out is this a hard rock to identify or is this something easy?
• 17:17
  SPEAKER_00: Like, is this something I've seen before or not?
• 17:19
  SPEAKER_00: And you were talking about the weathering on the surface.
• 17:21
  SPEAKER_00: Like, I sort of say, okay, you do that test.
• 17:24
  SPEAKER_00: First of all, this look this rock looks uh like something I haven't seen necessarily before.
• 17:28
  SPEAKER_00: Is that just weathering pattern on the surface?
• 17:30
  SPEAKER_00: I've broke if I break it open, is it gonna be granite and I know what granite is?
• 17:33
  SPEAKER_00: Like, is it hard or not?
• 17:34
  SPEAKER_00: Is it unique or not?
• 17:36
  SPEAKER_00: Is it a crazy weird rock?
• 17:38
  SPEAKER_00: And we've seen some crazy weird rocks at the various like old mine tailings piles that we found.
• 17:42
  SPEAKER_00: We've found weird minerals that you rarely find, right?
• 17:46
  SPEAKER_00: But then there's the common suite of rocks that are like the vast majority of rocks on earth are these 25 rocks that you you have your students identify, right?
• 17:54
  SPEAKER_00: So my first thing is like, is it one of the 25 or is it something completely weird and very like regionally focused?
• 18:00
  SPEAKER_00: So if I identify it's it's a rock I've seen before, one of the common ones, and it's sort of a unique take on one of the common ones.
• 18:08
  SPEAKER_00: I think I work very similarly through the process with just slightly different questions.
• 18:12
  SPEAKER_00: So the exactly the first thing you said is is it sedimentary or metamorphic or igneous?
• 18:17
  SPEAKER_00: I kind of say, is it banded or not?
• 18:20
  SPEAKER_00: Is there fine-scale structure to it?
• 18:22
  SPEAKER_00: Like is there layering in it?
• 18:23
  SPEAKER_00: And then it's either sedimentary or metamorphic.
• 18:25
  SPEAKER_00: Or if there's not structure to it, then it's either igneous or the unfoliated metamorphic rocks, right?
• 18:31
  SPEAKER_01: Um and so you're trying to classify it as well, right?
• 18:34
  SPEAKER_00: I'm classifying it very similarly, like we're working towards the same goal of igneous metamorphic or sedimentary, but with a different like starting question, I guess.
• 18:42
  SPEAKER_01: Yeah, let me interrupt you a second, because when I say our you're classifying the rock also, uh what we mean when we say that is we're we're not naming the rock, we're classifying it according to sedimentary, metamorphic, or igneous.
• 18:54
  SPEAKER_01: That's the classification.
• 18:55
  SPEAKER_01: I agree.
• 18:56
  SPEAKER_00: If you pick up a rock and you think, oh, I need to like right away determine this is a phonolite, I mean you're you're asking yourself to fail, right?
• 19:03
  SPEAKER_00: You are definitely going to misidentify this rock, like if you're asking that question first.
• 19:08
  SPEAKER_00: So I agree.
• 19:09
  SPEAKER_00: You you kind of start from really broad scale and then refine on your way down.
• 19:13
  SPEAKER_01: You brought up such a good point right there by mentioning a phonolite.
• 19:17
  SPEAKER_01: Okay, that that falls out of the normal category.
• 19:20
  SPEAKER_01: Totally.
• 19:20
  SPEAKER_01: Okay.
• 19:21
  SPEAKER_01: No intro-level geology class is ever going to talk about a phonolite.
• 19:25
  SPEAKER_01: But when you go to Devil's Tower and you look at the rocks there, it's a phonolite porphyry, but it looks just like a porphyrytic andesite.
• 19:35
  SPEAKER_01: They're both igneous rocks.
• 19:37
  SPEAKER_01: There are slight little nuances in the chemical composition, which makes it a phonolite and not an andesite.
• 19:43
  SPEAKER_01: And so that is not anything that I would ever expect anybody to be able to do in the field.
• 19:48
  SPEAKER_00: Right.
• 19:49
  SPEAKER_00: I agree completely.
• 19:50
  SPEAKER_00: This is definitely something that, you know, you take it, you get it igneous, and you say, My guess is it's a boophritic andesite, but I'm not sure.
• 19:57
  SPEAKER_00: You bring it back to the lab and you really nail the mineral identification.
• 20:00
  SPEAKER_00: And that kind of brings me to my next step, Chris.
• 20:02
  SPEAKER_00: Like I say, is there like structure to it?
• 20:05
  SPEAKER_00: And then that allows me to categorize on the left hand side it's sedimentary or metamorphic, and on the right hand side, it's igneous or maybe some of the metamorphic rocks.
• 20:14
  SPEAKER_00: Like it's a rare igneous rock that has centimeter scale layering in it, right?
• 20:18
  SPEAKER_00: Whereas almost all sediments have centimeter scale layering in it, and some metamorphic rocks have that.
• 20:23
  SPEAKER_01: What are you looking for to classify a rock as igneous?
• 20:27
  SPEAKER_00: What sells you?
• 20:28
  SPEAKER_00: Yeah, then it be so if I say structure, not structure, then I go to mineral identification.
• 20:32
  SPEAKER_00: Can I identify any minerals in this rock?
• 20:35
  SPEAKER_00: And if it's you know loaded with a bunch of feldspar and if it has amphibole in it, it's unlikely to be a metamorphic rock.
• 20:44
  SPEAKER_00: So if there's no structure to it and it's got a bunch of amphibole and biotite, it's probably not a metamorphic rock.
• 20:49
  SPEAKER_00: Maybe some of the weird ones are, but it's most likely an igneous rock.
• 20:53
  SPEAKER_00: Whereas on the flip side, if it does have structure and it's got a bunch of really fine-grained stuff and some sand grains in it, then it's probably a sedimentary rock, or maybe a little bit of a metamorphose sedimentary rock.
• 21:04
  SPEAKER_00: Or if there's internal structure and there's garnet in it, it's a metamorphic rock.
• 21:08
  SPEAKER_00: Like garnet is not a common sedimentary mineral.
• 21:10
  SPEAKER_00: So I kind of go jump right to mineral ID actually, after structure or not structure.
• 21:16
  SPEAKER_01: Um interesting.
• 21:17
  SPEAKER_01: That is a really interesting approach.
• 21:19
  SPEAKER_01: That's way different than me.
• 21:20
  SPEAKER_00: Yeah, it is.
• 21:21
  SPEAKER_00: So it's a curious.
• 21:22
  SPEAKER_00: This would be fun to go go look at rocks we don't know anything about together, right?
• 21:26
  SPEAKER_00: Yeah.
• 21:26
  SPEAKER_01: And I want to say too that I think one of the best exercises that you can do to kind of like test your knowledge and practice this process is going to a gravel pit.
• 21:35
  SPEAKER_01: Now, I know some of our listeners are like, what the heck is a gravel pit?
• 21:38
  SPEAKER_01: I've never, you know, you're not going to be a place where we're from.
• 21:43
  SPEAKER_01: That's true.
• 21:44
  SPEAKER_01: Um gravel pits are really awesome places to do this because you have this immense variety of rocks that are there that are mostly going to be rounded.
• 21:54
  SPEAKER_01: That's why it's in a gravel pit.
• 21:55
  SPEAKER_01: And so you got to break them open, and you kind of have to work through this protocol.
• 21:59
  SPEAKER_01: I remember an experiment.
• 22:00
  SPEAKER_01: Experience back when I was in college.
• 22:01
  SPEAKER_01: So this is eons ago.
• 22:04
  SPEAKER_01: You know, very very long time ago.
• 22:07
  SPEAKER_01: Back in the Mesozoic.
• 22:08
  SPEAKER_01: My petrology professor picked up, it was a knife, okay, and he just he picked it up at was holding his hands and he shoved it toward me and said, Hey, what is this?
• 22:19
  SPEAKER_01: First of all, I had all this pressure right there that I felt like, oh my gosh, you know, uh he just drodout called me out, uh which is one of the easiest rocks to identify, right?
• 22:28
  SPEAKER_01: But I kind of froze, and then I'm like, uh I don't know.
• 22:31
  SPEAKER_01: And he said, It's a nice and I immediately said, Well, how do you know that?
• 22:37
  SPEAKER_01: Because nobody had ever provided me with a plan for rock identification, which is why this is just something that I've put a lot of thought into.
• 22:47
  SPEAKER_01: I want to give young people, my students, I want to give them a protocol.
• 22:52
  SPEAKER_01: You're not just randomly sifting through a bunch of names.
• 22:56
  SPEAKER_01: There's a process for this.
• 22:57
  SPEAKER_01: Classify the rock first.
• 22:59
  SPEAKER_01: Here are my suggestions on how to do that, then name the rock.
• 23:04
  SPEAKER_00: Yeah, I agree with that completely, Chris.
• 23:06
  SPEAKER_00: I think it's a really useful exercise.
• 23:08
  SPEAKER_00: If you're listening to this and you don't know where to start, I think finding people who know a little bit or doing it with somebody, that's really helpful.
• 23:17
  SPEAKER_00: Like, you know, I learned a lot from you doing this on the various field trips that we went on.
• 23:22
  SPEAKER_00: I was a very annoying student, right?
• 23:24
  SPEAKER_00: Because I would just be like, No, you weren't.
• 23:26
  SPEAKER_00: Well, but okay, may some people might have considered me annoying, but it'd be like, hey, I would ask you a question and you'd say, Oh, you know, it's it's this, and I'd sort of say, Well, well, why?
• 23:35
  SPEAKER_00: Like, how do you know that?
• 23:36
  SPEAKER_00: Work me through that.
• 23:37
  SPEAKER_00: And I've stuck with that mentality all the way through graduate school.
• 23:41
  SPEAKER_00: Like anybody who's out in the field with me and they seem to know a rock that I don't, I'd say, how do you know that?
• 23:47
  SPEAKER_00: And figure out how they view this process.
• 23:50
  SPEAKER_00: I mean, some of the best learning I ever did was mapping where nobody knows what's going on in the region, and we're actually doing geological mapping, and we're it's just completely unknown.
• 23:58
  SPEAKER_00: But I'm with one of the best mappers in all of Canada.
• 24:02
  SPEAKER_00: So this woman who had mapped for 45 years in the north with a wide variety of rock types, and this was the most amazing learning experience because I got to understand how she works through this process, right?
• 24:13
  SPEAKER_00: Like, so just soaking that up from other people is the way to kind of learn from that.
• 24:18
  SPEAKER_00: And Chris, I think that I I keep coming back to this.
• 24:20
  SPEAKER_00: This would be so fun to go and do this again.
• 24:23
  SPEAKER_00: Like, I I can't get this out of my head that like you and I should go do this again, because it'd be really fun to kind of see how we work through it differently than than we did before, right?
• 24:31
  SPEAKER_00: I was admittedly young and quite ignorant at that point, and I think we've both seen a lot more rocks and a lot more different rocks since that time.
• 24:36
  SPEAKER_00: So this would be totally fun to kind of do again.
• 24:39
  SPEAKER_01: There is this pretty common saying in geology that the best geologist is the person who's seen the most rocks.
• 24:46
  SPEAKER_01: Oh, yes.
• 24:46
  SPEAKER_00: And there's a lot of validity to that.
• 24:49
  SPEAKER_00: There absolutely is a lot of validity.
• 24:51
  SPEAKER_01: The other thing that I want to talk about that is a little bit off topic, but you keep saying this, you've said it a number of times, that you were so annoying as a kid.
• 24:58
  SPEAKER_01: Now I just want to say that that's not true because what is annoying to me on field trips is when I'm treated like a tour guide.
• 25:07
  SPEAKER_01: When students or people treat me that way, I don't like that at all.
• 25:11
  SPEAKER_01: That's annoying to me.
• 25:13
  SPEAKER_01: I love curiosity.
• 25:14
  SPEAKER_01: I'm a curious guy, I want to know things.
• 25:16
  SPEAKER_01: Okay, and I love it then when students have that curiosity because that means they want to know.
• 25:22
  SPEAKER_01: They're curious about it, they are passionate about it.
• 25:25
  SPEAKER_01: And so I am the other way.
• 25:28
  SPEAKER_01: If I have to sit down a group of like students in the field and say, Listen, you guys are boring the heck out of me.
• 25:35
  SPEAKER_01: You know, that means they're not asking questions.
• 25:37
  SPEAKER_01: Yeah, you know, like I need that.
• 25:38
  SPEAKER_00: That's a good point.
• 25:39
  SPEAKER_00: That's a good point.
• 25:40
  SPEAKER_00: Yeah, I feel the same way.
• 25:41
  SPEAKER_00: There's nothing worse than a bunch of students who say, Oh, here's the rocks, you know, go identify them, and they just kind of wander around aimlessly, picking it up, writing things down, and don't really ask any questions.
• 25:51
  SPEAKER_00: And the best students are, in my experience, not the ones who get the A's.
• 25:55
  SPEAKER_00: They're the ones who pick up a rock and are like, Whoa, I don't know what this is.
• 25:59
  SPEAKER_00: This is so cool.
• 26:00
  SPEAKER_00: I gotta figure it out I gotta learn how to figure this out, who are kind of like really interested in working through it.
• 26:05
  SPEAKER_00: And they don't always get the best grades.
• 26:06
  SPEAKER_00: That's completely fine.
• 26:07
  SPEAKER_00: Like, I that's the most curious people.
• 26:09
  SPEAKER_01: So 100%.
• 26:11
  SPEAKER_01: Look, when you take a group of young people to the Tetons and you, you know, you have all this geology in front of you, and you you begin to talk through the geology of it.
• 26:19
  SPEAKER_01: How can they not have any questions about what's in front of them?
• 26:22
  SPEAKER_01: If they don't have any questions, then something's wrong.
• 26:25
  SPEAKER_01: And so, no, I I yeah, you need to stop saying that because you weren't annoying.
• 26:30
  SPEAKER_01: You were actually the opposite.
• 26:31
  SPEAKER_01: That's the first time that I actually saw your personality, you know, like seriously.
• 26:37
  SPEAKER_00: We're getting excited about rocks.
• 26:39
  SPEAKER_00: Yeah, it was.
• 26:40
  SPEAKER_00: So so Chris, I just want to come back to this like first definition.
• 26:45
  SPEAKER_00: The the first thing that I go through is like, is it a normal rock or a weird rock, right?
• 26:49
  SPEAKER_00: There's a lot of rocks that are very normal that look weird initially, and it's either weathering patterns or it's something that makes it look like gold or look like some really weird, really cool thing.
• 27:03
  SPEAKER_00: Whether it's shiny mica that has had some uh oxidation to it, right?
• 27:07
  SPEAKER_00: That is flaky and and is shiny.
• 27:10
  SPEAKER_00: People look at it, and it it is a beautiful mineral.
• 27:12
  SPEAKER_00: Like there's there's no doubt this is a beautiful mineral and it makes beautiful rocks, but it's also one of the most common minerals out there, right?
• 27:18
  SPEAKER_00: And it occurs everywhere.
• 27:19
  SPEAKER_00: And so it's important to identify that and also important to recognize that this is not a crazy unique rock.
• 27:26
  SPEAKER_00: And I think you probably get this a lot too, but I get emails from people being, you know, searchable on Penn State's website as a geology professor.
• 27:33
  SPEAKER_00: You get emails that are like, What's this rock?
• 27:36
  SPEAKER_00: And actually, the first question I ask myself is, is this a rock or not?
• 27:39
  SPEAKER_00: Is this slag?
• 27:40
  SPEAKER_00: Is this some weird concrete thing that they found in their backyard?
• 27:44
  SPEAKER_00: Right?
• 27:45
  SPEAKER_00: Like, is this actually a rock or not?
• 27:46
  SPEAKER_00: Is really one of the first questions.
• 27:48
  SPEAKER_01: That is such a good point.
• 27:50
  SPEAKER_01: It happens all the time where people bring in a piece of concrete, and concrete can be beautiful, actually.
• 27:56
  SPEAKER_01: It can, and it can be very confusing.
• 27:58
  SPEAKER_01: Yes, because it's loaded with real rocks and real minerals that are just kind of held together by you know by cement.
• 28:05
  SPEAKER_01: So it can that happens all the time.
• 28:08
  SPEAKER_00: I remember, Chris, when I was, I think I was after college or something.
• 28:12
  SPEAKER_00: There was uh one of your colleagues who thought it was quite good fun to sneak concrete into your rock garden and see how long it would take you to find it out, to figure out what somebody had snuck a big chunk of concrete in there.
• 28:23
  SPEAKER_00: That was we always got a kick out of that prank.
• 28:25
  SPEAKER_00: That was pretty.
• 28:25
  SPEAKER_01: He would always come into class too.
• 28:27
  SPEAKER_01: He he thought it was really funny.
• 28:28
  SPEAKER_01: He'd come in with a handful of gravel and he'd come into my room and interrupt me.
• 28:33
  SPEAKER_01: Um, you know, I'm hitting my mid stride, right?
• 28:35
  SPEAKER_01: And he interrupts you, he's like, Hey, can you please identify these rocks?
• 28:39
  SPEAKER_00: And then he would just laugh endlessly.
• 28:41
  SPEAKER_00: So yeah.
• 28:42
  SPEAKER_00: All right, so Chris, I want to wrap up this episode maybe with just like it's hard for people to know how to get started.
• 28:47
  SPEAKER_00: And it's hard when you're walking out there with zero knowledge, let's say, apart from listening to some episodes or a podcast.
• 28:53
  SPEAKER_00: What are the key things you should learn or or think about before you go out into the field and identify rocks?
• 28:59
  SPEAKER_00: Like, what do you need to kind of get started on this?
• 29:02
  SPEAKER_00: Is it sedimentary, igneous, or metamorphic process?
• 29:04
  SPEAKER_00: Because there's a little bit of a learning curve before you can do that, right?
• 29:08
  SPEAKER_00: And how would you Yeah, good question.
• 29:10
  SPEAKER_01: Really good question.
• 29:11
  SPEAKER_01: I think two things jumped to my mind.
• 29:14
  SPEAKER_01: One is get yourself familiar with the common sedimentary, the common metamorphic, and the common igneous rocks.
• 29:21
  SPEAKER_01: And we have these laid out beautifully.
• 29:23
  SPEAKER_01: I think beautifully, I'm tooting our own horn, but in Camp Geo.
• 29:27
  SPEAKER_01: So if you go to that, we have chapters that are devoted to the common types of all of these rocks with images that you need.
• 29:35
  SPEAKER_01: It's just a really good way to familiarize yourself with that, I think.
• 29:38
  SPEAKER_01: So that's the first thing that jumps to mind is get familiar with them.
• 29:41
  SPEAKER_01: The second thing is do your research before you go.
• 29:44
  SPEAKER_00: Totally.
• 29:44
  SPEAKER_00: I think I would agree completely with both those things.
• 29:47
  SPEAKER_00: I would slightly amend and say rocks and minerals.
• 29:49
  SPEAKER_00: And you know, learning the common minerals will help you as well.
• 29:53
  SPEAKER_00: And you don't really have to like know the difference between quartz and feldspar, but you kind of have to know I see something and it looks like quartz or feldspar.
• 30:00
  SPEAKER_00: You can kind of put those in the same bin.
• 30:02
  SPEAKER_00: But knowing the 10 minerals, and again, in Camp Geo, we cover that.
• 30:06
  SPEAKER_00: There's a lot of really good websites out there that have a bunch of images of different minerals as well.
• 30:10
  SPEAKER_00: It's a little bit hard to do without the rocks in your hand, but you can go to a little gem or mineral museum.
• 30:16
  SPEAKER_00: Like most universities will have a little gem and mineral display.
• 30:19
  SPEAKER_00: Penn State has this, it's open to the public.
• 30:21
  SPEAKER_00: Like go there, look at these things, and just learn as much as you can from books or websites.
• 30:26
  SPEAKER_00: And again, point us to Camp Geo.
• 30:29
  SPEAKER_00: That's a really we've done a good job of that, I think.
• 30:31
  SPEAKER_00: Even though it's not catered to mineral and rock identification, it is the intro geology course.
• 30:37
  SPEAKER_00: And so you get that information along with it, right?
• 30:40
  SPEAKER_00: Like learning how to identify these things is a key part of a geoscience education.
• 30:44
  SPEAKER_01: The only other thing I would add is settle down.
• 30:47
  SPEAKER_01: If you can't identify the rock, relax.
• 30:49
  SPEAKER_01: It doesn't mean that you don't know anything.
• 30:51
  SPEAKER_01: There are many uh an accomplished geologist that are out in the field that cannot identify the rock until they get it back in lab.
• 30:57
  SPEAKER_01: Oh, you know what?
• 30:58
  SPEAKER_00: There are the number of times I have thought a rock is one thing out in the field and then bring it back and it's something completely different.
• 31:04
  SPEAKER_00: I mean, that it happens more often than I would like to admit, but actually it happens to all the best field mappers too.
• 31:10
  SPEAKER_00: And I think the key thing is just be honest about that.
• 31:13
  SPEAKER_00: Like, I don't know what this mineral is, and I'm gonna need to do some homework to figure out what it is.
• 31:17
  SPEAKER_00: And a lot of that homework you've pointed out, like learn the regional geology, learn about the specific site.
• 31:21
  SPEAKER_00: And sometimes you'll find some weird stuff, but it's pretty rare to find a really, really totally unique thing that no one's known about or documented in that location before.
• 31:31
  SPEAKER_00: There are geologists who've been there before and have written something about it.
• 31:34
  SPEAKER_00: Cool, man.
• 31:35
  SPEAKER_00: Well, that's a big episode and a lot of stuff to to work through.
• 31:39
  SPEAKER_00: But I think we did a decent intro job, right?
• 31:42
  SPEAKER_01: I I hope so.
• 31:42
  SPEAKER_01: It only took us three years to get to this episode.
• 31:45
  SPEAKER_01: So Yeah.
• 31:46
  SPEAKER_00: And on that note, if you have questions, if you're listening to this and you have questions, you want uh sort of more information or you're learning this for the first time and you have some questions, you know, rock ID is always hard to do over an over an image sent to an email.
• 31:59
  SPEAKER_00: But if you have questions about the strategy or the differences between major rock types, hit us up.
• 32:03
  SPEAKER_00: We are planetgeocast at gmail.com.
• 32:05
  SPEAKER_00: All our social medias are at planet geocast.
• 32:07
  SPEAKER_00: Go to our website, planetgeocast.com.
• 32:10
  SPEAKER_00: There you can subscribe, support us.
• 32:12
  SPEAKER_00: We always love that.
• 32:13
  SPEAKER_00: And you can leave us a rating and a review on your podcast platform.
• 32:17
  SPEAKER_00: We always appreciate those.
• 32:18
  SPEAKER_01: Yeah.
• 32:19
  SPEAKER_01: Thanks, Richard, for the question.
• 32:20
  SPEAKER_00: Great questions, Richard.
• 32:22
  SPEAKER_00: Cheers.
• 32:23
  SPEAKER_00: Peace.