Igneous Rocks

Summary

This educational video delves into the world of igneous rocks, explaining their formation from cooled magma or lava. It distinguishes between intrusive rocks, formed slowly underground with large crystals like granite, and extrusive rocks, which form rapidly on the surface with small or no crystals, exemplified by basalt and obsidian. The video also highlights how the cooling rate affects crystal size and the presence of vesicles, providing a clear classification system for these rocks.

Takeaways

• 🌋 Minerals are the building blocks of rocks, and they combine in nature to form rocks.
• 📚 Rocks are classified based on their method of formation, not just color, texture, or density.
• 🔥 Igneous rocks form from the cooling and solidification of magma or lava.
• 🌐 There are three main types of rocks: igneous, sedimentary, and metamorphic.
• 🏔️ Intrusive igneous rocks form inside the Earth from magma and have large crystals.
• 🗻 Granite is an example of an intrusive igneous rock with visible mineral crystals.
• 🌀 Extrusive igneous rocks form on the Earth's surface from lava and have small or no crystals.
• 🌑 Obsidian is an extrusive igneous rock that cooled so quickly it has a glassy appearance and no visible crystals.
• 💭 Vesicular texture in igneous rocks indicates the presence of trapped gas bubbles.
• 📈 The reference tables provide a chart of common igneous rocks and their characteristics for further study.

Q & A

What are the building blocks of rocks?

Minerals are the building blocks of rocks, which make up their composition.

How many categories of rocks are there based on their method of formation?

There are three categories of rocks based on their method of formation: igneous, sedimentary, and metamorphic rocks.

What is an igneous rock?

An igneous rock is a rock that forms from the cooling and solidification of magma or lava.

What is the difference between magma and lava?

Magma is molten rock material found deep inside the Earth, while lava is magma that has erupted onto the surface.

What are the two types of igneous rocks based on where they cooled and solidified?

The two types of igneous rocks are intrusive igneous rocks, which form inside the Earth from magma, and extrusive igneous rocks, which form on the surface from lava.

Why do intrusive igneous rocks have large crystals?

Intrusive igneous rocks have large crystals because the magma cools slowly underground, allowing the minerals to form large crystals.

What is an example of an intrusive igneous rock and its visible minerals?

An example of an intrusive igneous rock is granite, which contains visible minerals like biotite mica (black), potassium feldspar (pink), and quartz (white).

What is the difference between extrusive igneous rocks and intrusive igneous rocks in terms of crystal size?

Extrusive igneous rocks have small or no crystals because they cool quickly on the surface, whereas intrusive igneous rocks have large crystals due to slow cooling underground.

What is the appearance of obsidian and why?

Obsidian has a glassy appearance because it cooled so quickly that no crystals were able to form at all.

What is the term for igneous rocks that have air bubbles trapped inside?

Igneous rocks with air bubbles trapped inside are called vesicular.

Where can we find a chart showing common igneous rocks and their characteristics?

A chart showing common igneous rocks and their characteristics can be found on page six of the reference tables mentioned in the script.

Outlines

00:00

🌋 Introduction to Igneous Rocks

The paragraph introduces the topic of igneous rocks and sets the stage for the video's content. It emphasizes the importance of minerals as the building blocks of rocks and discusses the classification of rocks based on their formation method. The paragraph outlines three main categories of rocks: igneous, sedimentary, and metamorphic. The focus then narrows to igneous rocks, explaining that they form from the cooling and solidification of magma or lava. The distinction between magma (below Earth's surface) and lava (on the surface) is highlighted, leading into a discussion of the two types of igneous rocks: intrusive and extrusive. Intrusive rocks, formed from slowly cooling magma deep within the Earth, are characterized by large mineral crystals, exemplified by granite. Extrusive rocks, formed from rapidly cooling lava on the surface, have small or no crystals and may contain trapped air bubbles, as seen in basalt and obsidian.

05:04

🔍 Characteristics of Igneous Rocks

This paragraph delves into the characteristics of igneous rocks, contrasting intrusive (plutonic) and extrusive (volcanic) types. Intrusive rocks, formed inside the Earth, have large crystals due to slow cooling processes, while extrusive rocks, formed at or near the surface, cool quickly and have small or no crystals, and may exhibit a vesicular texture from trapped gas bubbles. The paragraph concludes with a reference to a chart in the reference tables that lists common igneous rocks and their characteristics, indicating that this information will be studied in upcoming sessions.

Keywords

💡Minerals

Minerals are the naturally occurring, inorganic substances that have a specific chemical composition and crystalline structure. They are the fundamental building blocks of rocks, as mentioned in the script when discussing how rocks are formed from the combination of minerals in nature. For example, granite is composed of different minerals like biotite mica, potassium feldspar, and quartz.

💡Rocks

Rocks are naturally occurring solid substances composed of minerals. The video script discusses the classification of rocks based on their method of formation. Rocks are integral to the video's theme as they are the main subject being discussed.

💡Igneous Rocks

Igneous rocks are one of the three main types of rocks, as categorized by their formation process. They form from the cooling and solidification of magma or lava. The video focuses on igneous rocks, explaining how they are formed and classified into intrusive and extrusive types.

💡Magma

Magma is molten rock material found beneath the Earth's surface. It is a key component in the formation of igneous rocks, particularly intrusive igneous rocks, as explained in the script. Magma cools and solidifies slowly underground, leading to the formation of large mineral crystals.

💡Lava

Lava is molten rock material that has erupted onto the Earth's surface from a volcano. It is distinguished from magma by its location. The script explains that lava cools quickly, leading to the formation of extrusive igneous rocks with small or no visible crystals.

💡Intrusive Igneous Rocks

Intrusive igneous rocks, also known as plutonic rocks, form from magma that cools and solidifies slowly inside the Earth. The script uses granite as an example, noting that these rocks have large, visible crystals due to the slow cooling process.

💡Extrusive Igneous Rocks

Extrusive igneous rocks, also known as volcanic rocks, form from lava that cools and solidifies quickly on the Earth's surface. The script mentions basalt and obsidian as examples, noting that these rocks typically have small or no crystals and may be vesicular.

💡Crystals

Crystals are the solid, regular, geometric forms in which minerals can occur. The script explains that the size of crystals in igneous rocks is indicative of whether they are intrusive (large crystals) or extrusive (small or no crystals).

💡Vesicular

Vesicular refers to a texture found in some extrusive igneous rocks where gas bubbles become trapped as the lava cools quickly. The script describes how this can result in rocks with air bubbles trapped inside, contributing to the rock's texture.

💡Classification

Classification in the context of the script refers to the systematic grouping of rocks based on their formation process. The video script emphasizes that rocks are best classified by how they form, leading to the categorization into igneous, sedimentary, and metamorphic rocks.

💡Granite

Granite is an example of an intrusive igneous rock mentioned in the script. It is characterized by its speckled appearance due to large mineral crystals that are visible to the naked eye, indicating slow cooling from magma underground.

💡Basalt

Basalt is an example of an extrusive igneous rock discussed in the script. It is characterized by its fine-grained or glassy texture, resulting from rapid cooling of lava at the Earth's surface, which prevents the formation of large crystals.

Highlights

Minerals are the building blocks of rocks, forming through their combination in nature.

The best way to classify rocks is by their method of formation, not by color, texture, or density.

Rocks are classified into three categories: igneous, sedimentary, and metamorphic.

Igneous rocks are formed from the cooling and solidification of magma or lava.

The key difference between lava and magma: magma is beneath the surface, while lava is above the surface.

Two types of igneous rocks: intrusive (formed inside the Earth) and extrusive (formed on the surface).

Intrusive igneous rocks cool slowly, forming large crystals like granite.

Granite has visible mineral crystals like biotite mica, potassium feldspar, and quartz.

Intrusive rocks can have crystals larger than a millimeter, such as in pegmatite with centimeter-sized crystals.

Extrusive igneous rocks form on the surface, cooling quickly, leading to small or no crystals.

Extrusive rocks like basalt have tiny crystals smaller than a millimeter or none at all.

Obsidian cools so quickly that no crystals form, giving it a glassy appearance.

Vesicular texture is when air bubbles get trapped in extrusive rocks during rapid cooling.

Examples of vesicular rocks include those with air bubbles trapped in lava.

Summary: Intrusive igneous rocks cool slowly, forming large crystals; extrusive igneous rocks cool quickly, forming small or no crystals, sometimes with trapped air bubbles.

Transcripts

All right, in this video, we're going to talk about igneous rocks.

but before we can get into that, we have to step back a little bit.

We're going to be using our flow chart from class

So, let's get started.

And, of course, we know that minerals are the building blocks of rocks.

They are what make up rocks.

And so we're going to look at what happens when minerals combine in nature to form rocks.

But this brings up another question.

There are so many kinds of rocks, like this sandstone, and granite,

this piece of gneiss,

this piece of obsidian,

and shale and pumice.

All these rocks exist in nature, of course, along with thousands of other varieties.

So the question arises-- well, how do we classify them?

Do we group them by their color, their texture, their density?

What do we do?

Well, turns out that the best way to classify rocks is based on how they form,

the way in which they come to be.

So, let's add that to our sheet here.

This bubble under the word "rocks,"

we're going to write that they're classified based on their method of formation,

or, simply, how they form.

So if you do this classification, you will have three categories:

Igneous rocks, which we'll talk about today,

sedimentary rocks and

metamorphic rocks.

So, let's take a look at igneous rocks.

What, exactly, is an igneous rock?

An igneous rock is a rock that formed from the cooling and solidification of magma or lava.

Okay, let's add that.

They form from the cooling and solidification of lava or magma.

Now, what that means is that when molten rock cools down and essentially turns into a solid,

that is what an igneous rock is formed from.

When you think of lava and magma you probably picture this molten material in the crater of a volcano.

And that's exactly what we're talking about,

but what I want you to keep in mind Is that

there is a difference between Lava and Magma.

When it's deep inside the Earth, under the surface, we call it magma.

Once it erupts onto the surface, we call it lava.

Now, this material, whether inside the earth or on the surface, can cool and solidify.

So that gives us two different types of igneous rocks.

Igneous rocks are classified according to where exactly they did their cooling and solidifying.

So we have two types.

Let's start with the first type.

The first type of igneous rock is called an intrusive igneous rock .

That means it formed inside the earth from magma.

Now, as you can imagine, it's pretty hot inside the Earth

and so that magma is going to cool very slowly.

So magma cools slowly, and when it solidifies, it will allow minerals to form in crystals.

But because it happens so slowly, those crystals are able to grow very large.

So intrusive rocks are always going to have very large crystals.

Let's take a look.

This is a piece of granite.

What you'll notice is that it's speckled.

All of these speckles are different mineral crystals.

The black is biotite mica,

the pink is potassium feldspar,

the white is quartz.

But the fact that you can actually see them with the naked eye tells me

that they're big enough to have cooled slowly inside the earth

and that this is an intrusive rock.

If you want to know what I mean by "big,"

any crystals larger than one millimeter

signify that the rock is intrusive.

But, of course, we can get really giant crystals, like this pegmatite,

where the crystals might actually be bigger than, not a millimeter,

but an actual centimeter.

So, we're talking about very large crystals here.

Those are intrusive igneous rocks.

But what about the second type?

Well, as you might suspect, these are called extrusive igneous rocks.

Instead of forming deep underground and cooling slowly from magma,

these form on the surface and because they cool really quickly from lava

you're going to get small or no crystals at all.

As a result, they may even have air bubbles trapped inside,

which is something we call vesicular.

So, again, extrusive rocks form on the surface, very quickly,

and so you get very small or maybe even no crystals,

and they may have air bubbles trapped inside.

Let's take a look.

This is a rock called basalt.

And you'll notice that you can't really see any crystals at all.

If you look with a magnifying glass, you would find really tiny ones that are smaller than a millimeter.

That's a sign of an extrusive rock.

What about this obsidian? Now, this is interesting.

It cooled so quickly, in a matter of seconds,

that no crystals were able to form at all, and so you have this kind of glassy appearance.

Finally, if it cools quickly enough, you might get air bubbles trapped in the lava

and become part of the rock in the form of these vesicles, or vesicular texture.

You would look for air bubbles.

So, let's recap.

A quick review.

Igneous rocks formed from cooled and solidified magma or lava.

When it cools slowly, inside the earth,

we get intrusive, sometimes called plutonic, igneous rocks,

and they will have large crystals.

When lava cools quickly at or near the surface,

we'll get extrusive rocks, also called volcanic,

that will have small or no crystals.

They may be vesicular, meaning they have some trapped gas bubbles.

Page six of the reference tables shows our common igneous rocks and their characteristics,

and we'll be studying that chart in the coming days.

Thanks!