Rocks and Minerals
Grade 3 · Science · Study Guide
Learn how rocks form and what makes each mineral unique.
Rocks are everywhere — under your feet, in mountains, at the beach. But did you know that rocks are made of minerals? A mineral is a natural solid with a specific chemical makeup, like quartz or mica. Rocks are usually made of two or more minerals mixed together.
Geologists (scientists who study rocks) group rocks into three main types based on how they form. Igneous rocks form when melted rock called magma cools and hardens. Granite and obsidian are igneous rocks. When magma cools slowly underground, it forms large crystals. When it cools fast on the surface (from a volcano!), it forms small crystals or smooth glass like obsidian.
Sedimentary rocks form when layers of sand, mud, shells, or pebbles get pressed together over a very long time. Sandstone and limestone are sedimentary rocks. Fossils are most often found in sedimentary rock because the layers slowly buried and preserved ancient organisms.
Metamorphic rocks form when existing rocks are changed by intense heat or pressure deep inside the Earth. Marble (which comes from limestone) and slate are metamorphic rocks. The three rock types can change into each other over millions of years — this is called the rock cycle.
| Type | How It Forms | Examples |
|---|---|---|
| Igneous | Magma or lava cools and hardens | Granite, obsidian, basalt |
| Sedimentary | Sediment layers compress over time | Sandstone, limestone, shale |
| Metamorphic | Heat and pressure change existing rock | Marble, slate, quartzite |
Key terms
- mineral
- A natural solid found in Earth with a specific chemical composition
- igneous rock
- Rock formed when magma or lava cools and solidifies
- sedimentary rock
- Rock formed from compressed layers of sediment over time
- metamorphic rock
- Rock that has been changed by heat and pressure inside Earth
- rock cycle
- The ongoing process by which rocks change from one type to another
Flashcards
- igneous rock
- Rock formed from cooled magma or lava
- sedimentary rock
- Rock formed from compressed layers of sediment
- metamorphic rock
- Rock transformed by heat and pressure
- mineral
- A natural solid with a specific chemical makeup
- magma
- Melted rock beneath Earth's surface
- rock cycle
- The continuous process of rocks changing from one type to another
Practice questions
What type of rock forms when magma cools and hardens?
- Sedimentary
- Metamorphic
- Igneous
- Fossil
Show answer
Answer: Igneous
Igneous rocks form when magma (underground) or lava (at the surface) cools and solidifies. The word 'igneous' comes from the Latin word for fire.
Fossils are most commonly found in sedimentary rock.
Show answer
Answer: True
Organisms get buried in mud and sand that slowly turns to sedimentary rock. The rock preserves their shapes as fossils over millions of years.
The ongoing process by which rocks change from one type to another is called the rock ___.
Show answer
Answer: cycle
The rock cycle shows how igneous rocks can become sedimentary, sedimentary can become metamorphic, and any type can melt and become igneous again.
Which rock is an example of a metamorphic rock?
- Sandstone
- Granite
- Marble
- Obsidian
Show answer
Answer: Marble
Marble is a metamorphic rock that forms when limestone is subjected to intense heat and pressure. It's used in sculptures and buildings.
Rocks and minerals are the same thing.
Show answer
Answer: False
Minerals are individual natural substances with specific compositions. Rocks are made up of one or more minerals mixed together.
Fun facts
- The Hope Diamond is made of a mineral called diamond — the hardest natural substance on Earth!
- Some igneous rocks are so full of trapped gas bubbles that they can float on water — that's pumice!
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