What Type of Rock is this? — Transcript

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1. 0:00Hey everybody. In this video, we're
2. 0:02going to answer the question, what type
3. 0:04of rock is this?
4. 0:05We're going to take a look at all
5. 0:07different rocks, including igneous,
6. 0:09sedimentary, and metamorphic rocks. And
7. 0:12we're going to examine their
8. 0:13characteristics to determine which of
9. 0:15those three categories the rock falls
10. 0:17into.
11. 0:19Now, keep in mind, these are some very
12. 0:21loose characteristics, and we're going
13. 0:22to make some generalizations here. There
14. 0:25are exceptions to every rule, but if you
15. 0:27follow these basic characteristics, most
16. 0:29of the time you will make the right
17. 0:31identification. So, let's dive in.
18. 0:34We'll start by looking at some of these
19. 0:35key characteristics.
20. 0:37And we'll begin with igneous rocks. Now,
21. 0:39with igneous rocks, there are really
22. 0:41three main things to look for.
23. 0:43They tend to have intergrown crystals.
24. 0:45So, you'll see different mineral
25. 0:47crystals that are actually grown into
26. 0:49and attached to one another.
27. 0:52You might see a vesicular texture, which
28. 0:54simply means that there are trapped air
29. 0:56bubbles or gas pockets. And of course,
30. 0:58that forms when lava solidifies quickly
31. 1:01on the surface of the Earth.
32. 1:04Finally, if that lava cools fast enough,
33. 1:06you won't get any crystals or any air
34. 1:09bubbles, and the result will be a glassy
35. 1:11texture.
36. 1:12So, those are the three main
37. 1:13characteristics we look for for igneous
38. 1:15rocks. Crystals, vesicular texture, or a
39. 1:19glassy texture.
40. 1:20But what about sedimentary rocks? So,
41. 1:23these are rocks that form generally from
42. 1:25compacted and cemented sediments. So,
43. 1:28you're going to look for little grains
44. 1:30of sand, pebbles, clay, and silt,
45. 1:33different size chunks of rock that have
46. 1:35been squeezed together until they form
47. 1:38one larger rock.
48. 1:40We might also look for those sediments
49. 1:41to be forming in layers, and we might
50. 1:45keep our eye out for some sort of
51. 1:46fossils or other evidence of life,
52. 1:49including things like footprints, worm
53. 1:51trails, etc.
54. 1:54Finally, metamorphic rocks. These are
55. 1:57pretty tricky to identify, and a lot of
56. 1:59them might give you kind of a false
57. 2:01igneous identification. The one key
58. 2:04thing to look for with metamorphic rocks
59. 2:06will be banded crystals. So, we're
60. 2:08looking for these different, often
61. 2:10distorted, bands of crystals throughout
62. 2:13that are the result of the intense heat
63. 2:15and pressure that caused metamorphism.
64. 2:18So, let's look at some examples. On the
65. 2:20left here, I have my list of all the
66. 2:22different characteristics we just went
67. 2:24through, and we're going to pull some
68. 2:25rocks in, and we'll try and identify
69. 2:27them together. Let's begin.
70. 2:30Here's our first sample. Now, what jumps
71. 2:32out at me are these little air bubbles.
72. 2:35As we mentioned earlier, we call this a
73. 2:37vesicular texture, and so this is an
74. 2:39igneous rock. And if I had to justify
75. 2:42it, I would simply say this rock is
76. 2:44igneous due to its vesicular texture or
77. 2:47the trapped air bubbles or gas pockets.
78. 2:50Next.
79. 2:51This rock, if I look carefully, clearly
80. 2:54has fossils. These are fossils of some
81. 2:56fish that died perhaps in a shallow
82. 2:58lake, and their remains were imprinted
83. 3:01into the mud at the bottom and then
84. 3:02fossilized over many, many thousands of
85. 3:05years. So, this is clearly a sedimentary
86. 3:07rock because of the evidence of life or
87. 3:10the fossils that we see within it.
88. 3:14Next sample.
89. 3:15Here, this might be a little bit tricky,
90. 3:17but this is a great example of
91. 3:19intergrown crystals. I can see different
92. 3:22dark-colored crystals, probably the
93. 3:24mineral biotite mica, along with
94. 3:27lighter-colored minerals like quartz.
95. 3:29And all of the minerals are kind of
96. 3:30grown together, and so this must be an
97. 3:33igneous rock because of the intergrown
98. 3:35crystals.
99. 3:36If I want to go a little further, I can
100. 3:38hypothesize that this rock formed deep
101. 3:40within the earth, and I know that
102. 3:42because the crystals are large. And in
103. 3:44order for crystals to grow large, the
104. 3:47magma that created the igneous rock had
105. 3:49to cool slowly, and that likely took
106. 3:52place deep within the earth where it's
107. 3:53warmer.
108. 3:55Next up.
109. 3:57Take a look at this. What I see pretty
110. 3:59clearly are these different stripes or
111. 4:01what we call bands of crystals. And if
112. 4:04you look carefully at them, they're not
113. 4:06perfectly horizontal, they're wavy and
114. 4:08distorted. And so that is very clear
115. 4:11evidence that this is a metamorphic rock
116. 4:13as a result of the banded crystals. Now
117. 4:16remember, this forms when rocks are
118. 4:18exposed to intense heat or pressure and
119. 4:20that's what causes these bands to kind
120. 4:22of foliate and form.
121. 4:25Next, here I don't see any crystals, I
122. 4:29don't see any air bubbles, no compacted
123. 4:32sediments or evidence of life, no
124. 4:34banding, and so this is what we would
125. 4:36call a glassy texture and therefore it
126. 4:39is an igneous rock. This is the rock
127. 4:41obsidian, which forms when lava erupts
128. 4:44out of a volcano and cools really
129. 4:46quickly, not allowing any crystals to
130. 4:49form.
131. 4:51Next, if we take a close look at this
132. 4:53one, what we'll see is what looks like
133. 4:56individual sand grains that have been
134. 4:58squished and compacted together. And if
135. 5:00we could hold this in our hands, it
136. 5:02would feel just like sandpaper. And so
137. 5:04that tells me that we have a sedimentary
138. 5:06rock and I know it because it's made of
139. 5:08compacted and cemented sediments.
140. 5:13Here's another example of what we just
141. 5:15saw. These are also grains of sand that
142. 5:17have been compacted together. This is a
143. 5:19sandstone, so it's also sedimentary, but
144. 5:22it's got an added characteristic and
145. 5:24that is the sand has been deposited in
146. 5:26layers with slightly different colors.
147. 5:29And so I know that this is sedimentary
148. 5:31cuz it's got compacted sediments and
149. 5:33those sediments are layered. And what
150. 5:35you'll notice is that those layers are
151. 5:36perfectly flat, they're not distorted at
152. 5:39all, which tells me it's likely
153. 5:41sedimentary and not metamorphic.
154. 5:45Speaking of metamorphic, here's an
155. 5:47example of the rock gneiss, which is
156. 5:50metamorphic because it has banded
157. 5:52crystals. Now this might be a little
158. 5:54trickier because the layers the bands
159. 5:56are horizontal, they're not distorted at
160. 5:59all, but what tells me it's metamorphic
161. 6:01is that it's very crystallized and
162. 6:03that's going to occur as a result of
163. 6:04that metamorphic heat and pressure that
164. 6:07takes place deep within the earth.
165. 6:10So those are some examples for you. Just
166. 6:12to sum up our igneous rocks, we know
167. 6:15they're igneous because they have either
168. 6:16intergrown crystals, a vesicular
169. 6:19texture, or a glassy texture.
170. 6:21My sedimentary rocks are going to show
171. 6:23me compacted and cemented sediments,
172. 6:26perhaps layers of sediments, or some
173. 6:28evidence of life, whether it be fossils
174. 6:30or footprints or something along those
175. 6:32lines.
176. 6:33And finally, my metamorphic rocks are
177. 6:35going to display banding, banded
178. 6:38crystals that are often distorted.
179. 6:40If you'd like to test yourself, go find
180. 6:43my other video, which will give you an
181. 6:44opportunity to see if you can do this
182. 6:46identification on your own.
183. 6:48Thanks for watching and be sure to
184. 6:50subscribe and like.