Igneous Rocks Virtual Lab

^{Igneous rocks: Objective: Determine Identities of igneous Rocks.}

Objectives: In order to identify rocks:

• Define Igneous rocks

• Determine if rocks are intrusive or extrusive.

• Determine if rocks are coarse or fine grained

• Determine the silica content of rocks and how it is used to identify the rock.

Multiple Choice

Igneous rocks form when magma or Lava cools and forms crystals. Magma is melted rock located below the surface. Lava is melted rock located above the surface. What is seen in the image to this question

• Lava

• Magma

• Both

Multiple Choice

What is seen in this image under the volcano?

• Lava

• Magma

• Both

Multiple Choice

Intrusive igneous rocks cool underground. Deep in the crust, magma cools slowly. Slow cooling gives crystals a chance to grow. Intrusive igneous rocks have relatively large crystals that are easy to see. Where do intrusive rocks form?

• Deep in the crust

• On or near the surface

Multiple Choice

What type of crystals does intrusive rocks contain? (Hint refer to the previous question if needed)

• Large and easy to see

• Small and difficult to see

Multiple Choice

Extrusive igneous rocks form above the surface. The lava cools quickly as it pours out onto the surface. Extrusive igneous rocks cool much more rapidly than intrusive rocks. The rapid cooling time does not allow time for large crystals to form. Where do extrusive igneous rocks form?

• On the surface

• Deep in the Earth

Multiple Choice

What type of crystals forms in extrusive rocks? (Refer to previous slide if needed)

• Small

• Large

Coarse grained intrusive igneous rocks:

If the magma stays inside the earth and takes thousands of years to cool, it has time to make big crystals. These crystals make a coarse-grained igneous rock called an intrusive igneous rock. These coarse-grained crystals make the rock look sugary and speckled.

Fine grained, extrusive igneous rocks

When lava cools on top of the earth’s surface, it forms extrusive, or volcanic, igneous rock because it was extruded, or pushed, out onto the surface. Because it cools quickly, it only has time to make very tiny crystals. Extrusive, or volcanic, igneous rocks look dull and do not sparkle much because they are fine grained.

We call the individual mineral crystals in a rock the rock's grains.

• If the rock appears speckled it is coarse grained. Coarse grained rocks are intrusive.

• If the rock appears dull and mostly one color it is fine grained. Fine grained rocks are extrusive.

Multiple Select

Determine the classification of this igneous rock. You must choose TWO answers.

• Coarse grained

• Fine grained

• Intrusive

• Extrusive

Multiple Select

Determine the classification of this igneous rock. You must choose TWO answers.

• Coarse grained

• Fine grained

• Intrusive

• Extrusive

Multiple Select

Choose the three rocks that are coarse grained/intrusive rocks

Multiple Select

Choose the three rocks that are fine grained, extrusive rocks

One type of extrusive igneous rock cools so fast that mineral grains do not form at all. Instead it forms volcanic glass called obsidian.

What is Silica?

• Pure silica has the chemical formula SiO_2. - silicon dioxide.

• Pure silica is the mineral quartz

• Remember that a rock is a combination of minerals

• Think of silica as melted quartz.

• When a lot of melted quartz (silica) is in magma a light colored rock will form

• When less silica is in the magma dark colored rocks will form

• Rocks with more than 65 percent silica are light colored

• Those with between 45 and 55 percent silica are dark.

• The more silica, the lighter and visa versa.

Multiple Choice

Using the chart which intrusive rock is granite. Notice the arrows on the bottom of the chart that shows the silica content and lightness of the rock decreases moving from left to right. (Hint: Is granite the lightest or darkest according to the chart?)

Multiple Choice

Using the chart which intrusive rock is gabbro. Notice the bottom of the chart that shows the silica content and lightness or darkness of the rock. (click on the chart to make it bigger) (Hint: Is gabbro the lightest or darkest according to the chart?)

Multiple Choice

The amount of silica in a rock determines if the rock is light or dark colored. Remember the more silica the lighter the color of the rock. Which rock has a higher silica content?

Multiple Choice

Using the chart which extrusive rock is rhyolite. Notice the bottom of the chart that shows the silica content and lightness or darkness of the rock. (click on the chart to make it bigger) (Hint: Is rhyolite the lightest or darkest according to the chart?)

Multiple Choice

Using the chart which extrusive rock is basalt. Notice the bottom of the chart that shows the silica content and lightness or darkness of the rock. (click on the chart to make it bigger) (Hint: Is basalt the lightest or darkest according to the chart?)

Multiple Choice

Below are two volcanic rocks that formed from lava that erupted from a volcano. High silica content in volcanoes produce extremely violent eruptions. Which of these two volcanic rocks (1. Obsidian or 2. Pumice) formed during a violent eruption? (Hint: refer to slide 22)

Multiple Choice

Choose the answer that best explains your choice for slide 25.

• Obsidian is dark colored so that indicates it contains more silica

• Pumice is light colored so that indicates it contains more silica.

Multiple Select

Review: Choose all intrusive, coarse grained rocks. (Refer to previous slides if needed) (Choose TWO)

Multiple Select

Review: Choose all extrusive, fine-grained rocks. (Refer to previous slides if needed) (Choose TWO)