Studying rock formations helped researchers and geologists to know the historical information of the planet. Different kinds of rocks can tell different stories. For example, if you want to know more about the volcanic processes that took place on the planet millions of years ago, you might have to study igneous rocks.

What is an igneous rock?

Simply put, igneous rock is a rock type that is formed when lava or magma solidified. Molten magma is only formed when a rock, as well as other minerals around it, is exposed to high temperature (between 625 to 1,200° Celcius). Although magma stays molten underneath the Earth’s crust, they solidify and cool down when these objects are exposed to the surface or if there’s a change in temperature.

Igneous rock is considered a primary rock formation because it is formed from liquid. This is unlike sedimentary rock and metamorphic rock, which are both considered as a “derivative rock.” There are two kinds of igneous rock: intrusive and extrusive.

Intrusive and extrusive igneous rock

Intrusive igneous rock is formed when the magma solidifies within the crust. These rocks are also called plutons and are usually surrounded by rocks native to the area. This type of igneous rock is characterized by coarse texture and large crystals because of a slower cooling of the molten magma.

Extrusive igneous rock, on the other hand, is igneous rocks that are exposed to the surface and were cooled quickly. When a volcanic activity happens, the molten magma erupts to the surface. Instead of a coarse texture and crystal formation, extrusive igneous rocks form an amorphous glass.

The physical characteristics of igneous rock depend largely on whether it is formed exclusively or intrusively. Besides, the mineral contents are also taken into account when classifying these rocks. Here are the ten main characteristics of igneous rocks that make it stand out among other rock types existing on Earth.

Ten main characteristics of igneous rock

1. What makes an igneous rock?

The two main minerals of igneous rocks are silica and oxygen. Igneous rocks that are formed in lower temperatures tend to have these materials compared to others. On the other hand, high-temperature igneous rocks will likely have higher quantities of calcium, sodium, and iron in their composition.

2. Igneous rocks have no fossils inside.

Since igneous rock is formed when magma or lava solidifies, preserving fossils and other organic materials is not possible. The high temperature will destroy any organic material other than the minerals and the magma itself. Instead of igneous rock, fossils are usually found on sedimentary rocks.

3. There are over 700 types of igneous rock.

Igneous rocks can be classified into over 700 classifications. If you play Minecraft, you’re probably familiar with notable igneous rocks such as Andesite, Obsidian, Diorite, Granite,  and quartz. There is even a model called the Bowen Reaction series, which helps in classifying different igneous rocks based on different factors.

4. Igneous rocks are often classified by texture.

The texture of an igneous rock tells a lot about its chemical composition and how it is formed (whether intrusive or extrusive). As of now, there are six Igneous Rock textures used to classify different rocks. Some of these classifications are aphanitic (rapid lava cooling), vitreous (massive magma cooling), pegmatitic (the amount of other materials is massive), and phaneritic (rocks that are formed slowly for years.

5. Igneous rocks also have diverse silicon classification

Besides texture, location of cooling, and minerals, igneous rocks are also classified by its silicon content. There are five volcanic classifications used, as follows:

  • Felsic – at least 63% silica content
  • Intermediate – between 52% to 63% silica content
  • Mafic – between 45% to 52% silica content, with high iron content
  • Ultramafic Rock – less than 45% silica content
  • Alkalic – between 5-15% alkali content

6. Igneous rocks tend to have a moderate hardness score

Igneous rocks are quite durable and hard, a product of the chemical bonds that happened during its formation. To put it in context, the diamond, which is the hardest mineral on the planet, has a hardness of 10, while talc (the softest mineral) has a hardness of 1. Common igneous rocks like quartz and feldspar have a hardness score of 6.

7. Igneous rocks get stronger when transformed into metamorphic rock.

When rocks are exposed to high temperatures, the possibility of melting into magma is high. However, instead of melting, there is a possibility that rocks won’t melt. Instead, the mineral composition would change and become metamorphic rock. Most metamorphic rocks are harder than igneous rock.

8. Igneous rocks’ color is affected by mafic and felsic minerals.

The color of igneous rocks might vary from one rock to another. Based on Bowen’s Reaction series, mafic igneous rocks (silica with iron content) tend to have a darker color. Meanwhile, felsic igneous rocks (high silica content) tend to have a lighter color.

9. Igneous rocks are not reactive to acid.

Igneous rocks are not that reactive to acids. This is due to acids reacting well with carbonates (such as calcium, sodium, and potassium). Unlike sedimentary and metamorphic rocks, igneous rocks have very low carbonates content.

10. Igneous rocks have numerous uses.

There are several igneous rocks used in different industries. Granite, basalt, and pumice are some of the most commonly used igneous rocks. You can find these rocks in materials for buildings, kitchen worktops, decors, removing dead skin, construction materials, and more.

What characterizes igneous rocks?

Igneous rock, any of various crystalline or glassy rocks formed by the cooling and solidification of molten earth material. Igneous rocks constitute one of the three principal classes of rocks, the others being metamorphic and sedimentary.

What are the main properties of igneous rocks?

Igneous rocks contain randomly arranged interlocking crystals. The size of the crystals depends on how quickly the molten magma solidified: magma that cools slowly will form an igneous rock with large crystals. lava that cools quickly will form an igneous rock with small crystals.

What is unique about igneous rocks?

The magma, called lava when molten rock erupts on the surface, cools and solidifies almost instantly when it is exposed to the relatively cool temperature of the atmosphere. Quick cooling means that mineral crystals don’t have much time to grow, so these rocks have a very fine-grained or even glassy texture.

What are two key features of igneous rocks?

Characteristics of Igneous Rocks
  • The igneous form of rocks does not include any fossil deposits.
  • Most igneous forms include more than one mineral deposit.
  • They can be either glassy or coarse.
  • These usually do not react with acids.
  • The mineral deposits are available in the form of patches with different sizes.

What are the types of igneous rock?

The two main categories of igneous rocks are extrusive and intrusive. Extrusive rocks are formed on the surface of the Earth from lava, which is magma that has emerged from underground. Intrusive rocks are formed from magma that cools and solidifies within the crust of the planet.

What are called igneous rocks?

What are the uses of igneous rocks?

Igneous rock (derived from the Latin word ignis meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava.

Why are igneous rocks important?

The most common igneous rock found at the earth’s surface is granite. It is widely used in construction, granite contains crystals that are visible to the naked eye due to the very slow crystallization below the surface. Granite occurs in a range of vibrant colours.

What are the three types of igneous rocks?

Igneous rocks are also very important because their mineral and chemical makeup can be used to learn about the composition, temperature and pressure that exists within the Earth’s mantle. They can also tell us much about the tectonic environment, given that they are closely linked to the convection of tectonic plates.

What do igneous rocks look like?

When molten rock, or melted rock, solidifies, igneous rocks are formed. There are two types of igneous rocks: intrusive and extrusive.

Extrusive Igneous Rocks

  • andesite.
  • basalt.
  • dacite.
  • obsidian.
  • pumice.

What are some examples of extrusive igneous rocks?

Extrusive, or volcanic, igneous rocks look dull and do not sparkle much because they are fine grained. These crystals make a coarse-grained igneous rock called plutonic, or intrusive, igneous rock because the magma was intruded into cracks deep under the earth’s surface.

What are the 10 types of rocks?

Diamond is the hardest known mineral, Mohs’ 10.