Tag: science for kids

Learning about rocks and the rock cycle in your classroom this year? You may already know that there are three main types of rocks: igneous, sedimentary, and metamorphic. In this post, we will take a closer look at metamorphic rocks. Get ready to explore the formation, subtypes, properties, and examples of metamorphic rocks!

For Teachers: If you’re an educator planning to teach rocks, great visuals and activities are key to deepening understanding! Try my my Rocks Unit – a complete set of all the printable worksheets, activity directions, and visuals you’ll need (plus you’ll support this blog with your purchase! ❤️)

How do metamorphic rocks form?

Metamorphic rocks form deep below the Earth’s surface. Metamorphic rocks form when other rocks experience lots of heat and pressure underground. The heat comes from the Earth’s interior and the pressure comes from the weight of overlying layers of rock and sediment.

Every metamorphic rock was once a different rock, called the parent rock, or protolith. The protolith can be sedimentary, igneous, or even a different metamorphic rock. For example, when the sedimentary rock sandstone is exposed to intense heat and pressure, it can become the metamorphic rock quartzite. This transformation, called metamorphism, forces the minerals in the parent rock to reorganize into a more compact structure, making metamorphic rocks quite sturdy and dense.

Metamorphism can only happen when the amount of heat and pressure are just right. If there is too little heat and pressure, metamorphism will not happen. If the heat and pressure grow too high, the rock will melt into magma instead.

Properties of Metamorphic Rocks

There are many different metamorphic rocks, and they do not all look the same. Shimmering schist, sturdy slate, and glimmering marble are all metamorphic! Their varied appearances are influenced by several properties including their mineral composition, grain (crystal) size, and foliation. Let’s learn some more about each of these properties…

Grain Size

Metamorphic rocks are made of crystals of minerals. Crystals come in different sizes. Rocks with large crystals can appear sparkly or shimmery, like schist or marble. But not all crystals are big. In fact, some rocks are made of crystals so tiny that you need a microscope to see them. Rocks made of microscopic crystals may appear more dull.

In general, bigger crystals form under higher heat and pressure. A rock with large, visible crystals formed under higher heat and pressure than a rock made of tiny crystals.

Foliation

Some (but not all) metamorphic rocks have foliation – which means banding or layering. Foliation presents in several different ways, depending on the conditions while the rock is formed and the mineral crystals in the rock. A foliated rock with large crystals formed under high heat and pressure. This rock may appear to have bands or stripes of different colored mineral crystals. An example of this is gneiss, which appears to have alternating bands of light and dark crystals. However, a foliated rock with microscopic crystals formed under lower heat and pressure. This rock may appear to be made of layers or plates, like slate.

Metamorphic Subtypes

There are two types of metamorphic rocks: foliated and nonfoliated. With a little practice, you can learn to tell them apart. Let’s learn a little more about each.

Metamorphic Foliated

Metamorphic foliated rocks have bands or layers. Some, like gneiss, have alternating bands of light and dark crystals. Others, like phyllite and slate, look like they are made of sheets or layers. Foliation forms when a rock is being squeezed hardest in a particular direction rather than from all sides. This may happen when a rock is buried deep underground. The directed pressure forces the minerals to line up in the same direction, creating the bands or layers.

Metamorphic Nonfoliated

Metamorphic nonfoliated rocks form when the pressure comes from all sides or if the minerals do not line up. Consequently, nonfoliated rocks do not have bands or layers. Instead, nonfoliated rocks are usually a single solid color and made of interlocking mineral crystals. These crystals can be quite large or appear fine-grained. Some nonfoliated rocks, like marble, are prized for their strength and beauty, which makes them popular in construction and fine arts.

Examples of metamorphic rocks

Here are some examples of common metamorphic rocks. If you’re studying rock identification or creating a rock collection, you’ll want to make sure to examine the following rocks:

Foliated Rocks

• Gneiss
• Schist
• Phyllite
• Slate

Nonfoliated Rocks

• Marble
• Quartzite
• Hornfels

What’s Next?

For everyone: there’s more to learn about rocks! Take a closer look at igneous rocks or sedimentary rocks. Or, continue reading more about the rock cycle or the difference between rocks and minerals.

For educators: check out my posts on how to set up a rock ID lab activity, directions for a fun rock ID review bingo game, and a list of rock and mineral activity ideas that you can try in your classroom!

Study this topic with Wild Earth Lab!

I’ve already created an easy way for you to make teaching rocks & minerals in your classroom fun and engaging! This set includes all the printable materials you need for studying rocks and minerals, including diagrams, readings, activity directions, and worksheets!

Explore more lessons from Wild Earth Lab:

If you enjoyed this post, I know you will love trying my other printable science and nature units in your classroom too!

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References and Further Reading

1. Earle, S. (2019). Physical Geology. BCcampus Open Education. (Chapters 2-7). Available: https://opentextbc.ca/physicalgeology2ed/
2. Johnson, C., Affolter, M.D., Inkenbrandt, P., & Mosher, C. (2017). An Introduction to Geology. Salt Lake Community College. (Chapters 3-6). Available: https://opengeology.org/textbook/
3. Jones, C. E. (n.d.). Igneous Textures. University of Pittsburg. Department of Geology and Planetary Science. Available: https://sites.pitt.edu/~cejones/GeoImages/2IgneousRocks/IgneousTextures.html
4. Plummer C.C., Carlson D.H., & Hammersley L. (2019). Physical Geology. McGraw-Hill Education. (Chapters 1-7).

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Are you ready to learn all about rocks and the rock cycle in your classroom this year? If so, it’s important to know all about the three main types of rocks: igneous, sedimentary, and metamorphic. In this post, we will take a closer look at sedimentary rocks. Get ready to learn all about the formation, subtypes, properties, and examples of sedimentary rocks!

For Teachers: If you’re an educator planning to teach rocks, great visuals and activities are key to deepening understanding! Try my sedimentary rock printables, also found within my complete Rocks Unit – a complete set of all the printable worksheets, activity directions, and visuals you’ll need (plus you’ll support this blog with your purchase! ❤️)

How do sedimentary rocks form?

Sedimentary rocks form at or near the Earth’s surface.  They form from deposits of sediments, minerals, and/or organic matter.

On the Earth, forces like water and shifting temperatures work endlessly to break rocks down. The tiny broken-down pieces of rocks are called sediments. Some of the minerals in rocks may also dissolve in water, the same way sugar dissolves in tea. We call the dissolved minerals solutes.

Sediments and solutes move and are deposited in new places through a process called erosion. As sediments build up, something special happens. Sediments compact together under their own weight or are cemented together by crystallizing minerals. This forms new rocks, known as sedimentary.

Properties of Sedimentary Rocks

There are many different sedimentary rocks, and they do not all look the same. Soft mudstones, rough sandstones, and even coal are all sedimentary! Their varied appearances are influenced by several properties including their mineral makeup and grain (sediment particle) size. Let’s learn more about some of the properties of sedimentary rocks…

Sedimentary Grain Sizes

You already know that many sedimentary rocks are made from compacted and cemented sediments. The size of those sediments determines the type of sedimentary rock. Mudstones are made from the tiniest clay particles that are so small you cannot see them. Sandstones are made from little grains of sand, which you can see with your naked eye if you look at them up close. Conglomerate and breccia are made from the largest sediments – like gravel and small pebbles.

Geologists call the size of the particles in a rock the “grain size”. Grain size is important because it impacts the porosity and permeability of a rock. Very porous rocks like sandstone and conglomerate make good aquifers that store water underground. Do you know where your drinking water comes from? If you drink well water, then your drinking water comes from an aquifer!

Sedimentary Composition

Sedimentary rocks contain compacted and cemented grains, crystals of mineral precipitates, or sometimes organic materials. However, each rock has its own special blend of minerals.

Some sedimentary chemical rocks (those made from recrystallized solutes) contain carbonates. Carbonates are minerals that react with acid – just like how baking soda reacts with vinegar. Geology students find out if a rock contains carbonates by placing a drop of acid on the rock and watching for bubbling or fizzing. Rocks that fizz or bubble in a reaction with acid contain carbonates.

Other sedimentary rocks contain organic carbon and consequently burn. Geologists test for organic matter by attempting to combust a rock. The organic matter in the rock will burn in a combustion reaction – allowing the geologist to see how much of the rock was organic.

Sedimentary Subtypes

There are several subtypes of sedimentary: clastic, chemical, organic, and biochemical. They are formed from different materials. Let’s learn a little more about each.

Sedimentary Clastic Rocks

Sedimentary clastic rocks, such as sandstone and siltstone, form from tiny solid particles of rock called sediments. Sediments form through a process called weathering, in which rocks break down over time into smaller pieces. These pieces move around thanks to forces like flowing water, wind, and gravity, eventually coming together to form new rocks.

But how do loose sediments become a solid rock? Two processes, compaction and cementation, are responsible. Compaction happens when sediments are buried and pressed into a rock by the weight above. Cementation happens when water evaporates, leaving behind minerals that act like cement, holding the sediments together. Clastic rocks vary in their grain sizes, from microscopic particles in mudstone to large gravel pieces in breccia and conglomerates.

Sedimentary Chemical Rocks

Have you ever stirred sugar into water until it disappears?  Although you cannot see the sugar, it is still there, dissolved in the water. Like sugar, many minerals dissolve in water too! Most liquid water on Earth contains dissolved minerals.

Now perhaps you are wondering: how does water make rocks? Imagine an ancient ocean, with water rich in dissolved minerals. As time passes, the ocean begins to shrink, eventually drying up completely. When the water evaporates, the minerals from the water recrystallize to form sedimentary chemical rocks. This process, called precipitation, is the opposite of dissolving. Sedimentary chemical rocks are crystalline but often look fine-grained. Some are made of carbonate and react strongly to acid. Rock salt and limestone are two examples of sedimentary chemical rocks.

Sedimentary Organic Biochemical Rocks

Sedimentary organic and biochemical rocks are similar to sedimentary clastic rocks. However, they aren’t composed of sediments but rather form from buried plant and animal matter. Through compaction and cementation, the matter eventually becomes rock. Examples include coal, formed from compressed plant matter, and coquina, made of compacted and cemented shell fragments. These rocks can tell us fascinating stories about life on Earth in prehistoric times!

Examples of sedimentary rocks

Here are some examples of common sedimentary rocks. If you’re studying rock identification or creating a rock collection, you’ll want to make sure to examine the following rocks:

Clastic Rocks

• Mudstone
• Siltstone
• Sandstone
• Conglomerate
• Breccia

Chemical Rocks

• Limestone
• Rock salt
• Chert
• Ironstone

Biochemical and Organic Rocks

• Fossiliferous Limestone
• Coquina
• Diatomite
• Anthracite
• Coal

What’s Next?

For everyone: there’s more to learn about rocks! Take a closer look at igneous rocks. Or, continue reading more about the rock cycle or the difference between rocks and minerals.

For educators: check out my posts on how to set up a rock ID lab activity, directions for a fun rock ID review game, and a list of rock and mineral activity ideas that you can try in your classroom!

Study this topic with Wild Earth Lab!

I’ve already created an easy way for you to make teaching rocks & minerals in your classroom fun and engaging! This set includes all the printable materials you need for studying rocks and minerals, including diagrams, readings, activity directions, and worksheets!

Explore more lessons from Wild Earth Lab:

If you enjoyed this post, I know you will love trying my other printable science and nature units in your classroom too!

---

Are you interested in reading more posts like this? Subscribe or follow Wild Earth Lab using the links below!

• Facebook
• Instagram
• Pinterest
• Etsy

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References and Further Reading

1. Earle, S. (2019). Physical Geology. BCcampus Open Education. (Chapters 2-7). Available: https://opentextbc.ca/physicalgeology2ed/
2. Johnson, C., Affolter, M.D., Inkenbrandt, P., & Mosher, C. (2017). An Introduction to Geology. Salt Lake Community College. (Chapters 3-6). Available: https://opengeology.org/textbook/
3. Jones, C. E. (n.d.). Igneous Textures. University of Pittsburg. Department of Geology and Planetary Science. Available: https://sites.pitt.edu/~cejones/GeoImages/2IgneousRocks/IgneousTextures.html
4. Plummer C.C., Carlson D.H., & Hammersley L. (2019). Physical Geology. McGraw-Hill Education. (Chapters 1-7).

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Are you studying rocks and the rock cycle in your classroom this year? If you’re ready to take a deep dive into all things rocks, it’s important to know all about the three main types of rocks: igneous, sedimentary, and metamorphic. In this post, we will take a closer look at igneous rocks. Get ready to learn all about the formation, subtypes, properties, and examples of igneous rocks!

For Teachers: If you’re an educator planning to teach rocks, great learning resources are key to deepening understanding! I think you and your students will love my complete Rocks Unit – a set of all the printable worksheets, activity directions, and visuals you’ll need (plus you’ll support my blog with your purchase! ❤️)

How do igneous rocks form?

All igneous rocks form from molten rock. When molten rock is underground, we call it magma. Molten rock is only called lava when it’s on Earth’s surface. The intense pressure and heat deep underground keep magma in the molten (liquid) form. However, when the heat and pressure lessen, the molten rock solidifies, forming crystals. This can happen very slowly while the rock is still underground. If the molten rock reaches the Earth’s surface, it cools much more rapidly. This is because the surface of the Earth is very cool compared to the Earth’s insides.

Properties of Igneous Rocks

There are many different igneous rocks, and they do not all look the same. Bubbly pumice, smooth obsidian, and sparkly granite are all igneous rocks! Their varied appearances are influenced by their mineral makeup and the specific conditions during their formation. Igneous rocks come in a wide variety of different textures and compositions. Let’s learn more about both of these properties…

Igneous Textures

As molten rock cools, it forms crystals. The size of these crystals depends on how quickly the rock cools. Slow cooling provides time for big, interlocking crystals to form. Rapid cooling makes tiny, fine-grained crystals. We use special terms to describe these different textures: phaneritic (big crystals), aphanitic (tiny crystals), and porphyritic (a mixture of both).  But that’s not all! Some lava rocks, like pumice, have a bubbly texture filled with tiny holes. Others, like obsidian, are smooth and look glassy. There are even rocks made of many pieces of volcanic debris all stuck together, giving them what is known as a pyroclastic texture.

Igneous Compositions

Igneous rocks also come in different colors, which can tell us a lot about the minerals inside them – i.e., their mineral compositions. Light-colored minerals rich in silicon and oxygen are called felsic minerals. Rocks with lots of felsic minerals, like granite and rhyolite, are usually light and warm in color. On the other hand, dark-colored minerals rich in iron or magnesium are called mafic minerals. Rocks with lots of mafic minerals, like gabbro and basalt, are mostly dark gray, black, or green.

Subtypes

There are two main subtypes of igneous rocks: intrusive and extrusive. The main difference between them is where they form. Intrusive rocks form within the Earth while extrusive rocks form on the Earth’s surface.

Igneous Intrusive Rocks

More specifically, an igneous intrusive rock starts as magma, which is what we call molten rock located underground. The magma is insulated deep within the Earth, so it cools very slowly. The slow cooling allows plenty of time for large interlocking crystals to form. Granite, diorite, and gabbro are examples of igneous intrusive rocks.

Igneous Extrusive Rocks

In contrast, igneous extrusive rocks form when hot lava cools on the Earth’s surface such as when a volcano erupts. Lava cools very quickly on the surface, so there is not enough time for big crystals to form. If you are trying to decide if an igneous rock is intrusive or extrusive, texture is your biggest clue! While intrusive rocks are always made of large interlocking crystals, extrusive rocks come in a variety of other textures: fine-grained, glassy, bubbly, and more! Basalt, rhyolite, and pumice are igneous extrusive rocks.

Examples of igneous rocks

Here are some examples of common igneous rocks. If you’re studying rock identification or creating a rock collection, you’ll want to make sure to examine the following rocks:

Aphanitic or Porphyritic Rocks

• Granite
• Diorite
• Gabbro
• Peridotite

Phaneritic Rocks

• Rhyolite
• Andesite
• Basalt

Vesicular Rocks

• Pumice
• Basalt
• Scoria

Others (pyroclastic & glassy)

• Tuff
• Volcanic Breccia
• Obsidian

What’s Next?

For everyone: there’s more to learn about rocks! Continue reading more about the rock cycle or the difference between rocks and minerals.

For educators: check out my posts on how to set up a rock ID lab activity, directions for a fun rock ID review game, and a list of rock and mineral activity ideas that you can try in your classroom!

Study this topic with Wild Earth Lab!

There’s no need to scramble to put together the perfect rocks lesson  – I’ve already created it for you! This set includes all the printable materials you need for studying rocks and minerals.

Explore more lessons from Wild Earth Lab:

If you enjoyed this post, I know you will love trying my other printable science and nature units in your classroom too!

---

Are you interested in reading more posts like this? Subscribe or follow Wild Earth Lab using the links below!

• Facebook
• Instagram
• Pinterest
• Etsy

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References and Further Reading

1. Earle, S. (2019). Physical Geology. BCcampus Open Education. (Chapters 2-7). Available: https://opentextbc.ca/physicalgeology2ed/
2. Johnson, C., Affolter, M.D., Inkenbrandt, P., & Mosher, C. (2017). An Introduction to Geology. Salt Lake Community College. (Chapters 3-6). Available: https://opengeology.org/textbook/
3. Jones, C. E. (n.d.). Igneous Textures. University of Pittsburg. Department of Geology and Planetary Science. Available: https://sites.pitt.edu/~cejones/GeoImages/2IgneousRocks/IgneousTextures.html
4. Plummer C.C., Carlson D.H., & Hammersley L. (2019). Physical Geology. McGraw-Hill Education. (Chapters 1-7).

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