Video Transcript
Which of the following is not a
difference between plutonic and volcanic rocks? (A) Plutonic rocks are formed from
the slow cooling of magma, while volcanic rocks are formed from the quicker cooling
of lava. (B) Plutonic rocks are igneous
rocks, while volcanic rocks are sedimentary rocks. (C) Plutonic rocks contain large
crystals, while volcanic rocks contain small crystals. (D) Volcanic rocks often contain
small holes from the extrusion of gases as they cool, while plutonic rocks do
not. (E) Plutonic rocks are formed deep
underground, while volcanic rocks are formed on the surface.
This question has to do with the
differences between plutonic and volcanic rocks. Both plutonic and volcanic rocks
are types of igneous rock. Igneous rocks are rocks formed from
the cooling and solidification of molten material from below Earth’s crust. When this molten material is below
the surface of the Earth, it’s referred to as magma. And when it’s above the surface of
the Earth, it’s called lava. As magma is found in the lower part
of the Earth’s crust and the upper part of the mantle, it has a high ambient
temperature and cools very slowly.
The slow cooling process allows for
the formation of large crystals. The type of igneous rock formed
when magma slowly cools is called plutonic rock. Unlike magma, lava on the surface
cools quickly. As lava cools much more rapidly,
there isn’t sufficient time for large crystals to grow. Thus, small crystals are
formed. In addition, when magma reaches the
surface and becomes lava, gases in the magma are able to escape. The process of gases escaping often
creates small holes in the rocks as the lava cools. The type of igneous rock formed
when lava cools is called volcanic rock.
Now that we know more about
volcanic and plutonic rocks, we can look at the answer choices and identify which is
not a difference between the two. We can eliminate answer choice (A)
as plutonic rocks are formed from the slow cooling of magma, while volcanic rocks
are formed from the quicker cooling of lava.
Answer choice (B) describes
plutonic rocks as igneous rocks and volcanic rocks as sedimentary rocks. However, we know that both plutonic
and volcanic rocks are igneous rocks. Therefore, answer choice (B) is
likely the answer to this question. But just to be sure, let’s take a
look at the other answer choices.
We can eliminate answer choice (C)
as plutonic rocks do contain large crystals, while volcanic rocks contain small
crystals.
We can eliminate answer choice (D)
as volcanic rocks do often contain small holes from the extrusion of gases, while
plutonic rocks do not.
We can also eliminate answer choice
(E) as plutonic rocks are formed when magma cools deep underground, while volcanic
rocks are formed when lava cools on the surface.
In conclusion, the statement that
is not a difference between plutonic and volcanic rocks is answer choice (B). Plutonic rocks are igneous rocks,
while volcanic rocks are sedimentary rocks.
