Rocks

Rocks

Multiple Choice

Marcie is hiking in the mountains and she discovers an interesting shiny rock. As she picks it up she wonders whether it could be a mineral or whether it is just a rock. She notes that it is solid and naturally occurring with a definite chemical composition, but that it has no definite crystal structure. Suppose the object Marcie found is a rock formed by volcanic processes. What type of rock would it be?

• igneous

• metamorphic

• mineral

• sedimentary

Volcanic rock is igneous rock formed from cooled magma or lava. If you chose “mineral,” recall that not all rocks are minerals, even if they are shiny. Metamorphic rock is rock that undergoes change, and sedimentary rock is formed of sediments that are pressed together to form rock over many years.

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Explanation

Multiple Choice

Marcie believes that she has found a piece of obsidian.

What causes obsidian to form?

• extremely hot rock that cools fast

• remains of plants and animals compacted

• pressure deep beneath the surface of Earth

• particles of rocks pressed and cemented together

Obsidian is formed by rapidly cooling lava. This is what gives it its shiny, glass-like appearance. Compaction and cementation are ways that sedimentary rocks form. Pressure is how metamorphic rock is formed from the heat and pressure beneath Earth’s surface.

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Explanation

Multiple Select

Jill is planting a garden in her yard and notices that the fertilizer she is using contains gypsum. She learns that gypsum is a rock that is mined from underground and used to make fertilizer and other products. She remembers from science class that gypsum is rated a 2 on Moh’s hardness scale.

Which of these describes this rock? Choose the two statements that apply.

• It cannot scratch any other rocks.

• It can scratch rocks that are rated a 1.

• It is very soft compared to other rocks.

• It is very hard compared to other rocks.

• It can scratch any rock rated from a 2 to a 10, but not a 1.

Mohs hardness scale goes from 1 to 10, with 1 being the softest and 10 being the hardest rock. Since gypsum is a 2, it would only be able to scratch rocks rated as 1, and it would also be soft compared to most other rocks. Remember that all rocks can scratch rocks with lower hardness ratings. Also, remember that the higher the number, the harder the rock.

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Explanation

Open Ended

Explain how metamorphic rock is formed.

Metamorphic rocks are formed under enormous heat and pressure beneath the surface of Earth. They undergo a change just like organisms that go through the process of metamorphosis.

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Explanation

Poll

How ready do you feel for the quiz tomorrow?