Minerals and the Rock Cycle

Grade 6 · Science · Study Guide

Learn how minerals form rocks and how rocks continuously change through the rock cycle.

Minerals are naturally occurring, inorganic solids with a definite chemical composition and a crystalline structure. Over 4,000 minerals have been identified on Earth. Rocks are made up of one or more minerals. Geologists identify minerals by their properties, including hardness (using the Mohs scale), luster, color, streak, and cleavage.

Rocks are classified into three main types based on how they form. Igneous rocks form when magma (molten rock underground) or lava (molten rock at the surface) cools and solidifies. Granite and basalt are common igneous rocks. Sedimentary rocks form when layers of sediment — particles of rock, sand, or organic material — are compacted and cemented together over time. Limestone and sandstone are examples. Metamorphic rocks form when existing rocks are changed by heat and pressure deep within the Earth without fully melting. Marble (from limestone) and slate (from shale) are metamorphic rocks.

The rock cycle describes how rocks continuously transform from one type to another over millions of years. Igneous rock can be weathered into sediment, which becomes sedimentary rock. Sedimentary rock buried deep underground can be transformed into metamorphic rock. Metamorphic rock can melt into magma, which cools to form new igneous rock. This cycle never stops — Earth's rocks are constantly being recycled.

Key terms

Mineral: A naturally occurring, inorganic solid with a definite chemical composition and crystalline structure.
Igneous rock: Rock formed when magma or lava cools and solidifies.
Sedimentary rock: Rock formed when layers of sediment are compacted and cemented together over time.
Metamorphic rock: Rock formed when existing rocks are changed by heat and pressure without melting.
Rock cycle: The continuous process by which rocks change from one type to another through geological processes.
Mohs hardness scale: A scale from 1 to 10 that rates a mineral's resistance to scratching, with talc (1) being softest and diamond (10) hardest.

Flashcards

Mineral: Naturally occurring, inorganic, solid with definite chemical composition and crystal structure.
Igneous rock: Forms from cooled magma (intrusive) or lava (extrusive); examples: granite, basalt, obsidian.
Sedimentary rock: Forms from compacted and cemented sediment layers; examples: sandstone, limestone, shale.
Metamorphic rock: Forms from existing rocks altered by heat and pressure; examples: marble, slate, quartzite.
Rock cycle: The continuous transformation of rocks among igneous, sedimentary, and metamorphic types.
Weathering: The breaking down of rocks at the surface by water, wind, ice, or chemical reactions.
Erosion: The movement of weathered rock particles by water, wind, or ice to a new location.
Magma vs. lava: Magma is molten rock below Earth's surface; lava is magma that reaches the surface.

Questions

Which type of rock forms when lava cools and solidifies on Earth's surface?
1. Sedimentary
2. Metamorphic
3. Igneous
4. Mineral
Show answer
Answer: Igneous
Igneous rocks form when magma or lava cools and solidifies. Extrusive igneous rocks (like basalt) form from lava cooling on the surface; intrusive igneous rocks (like granite) form from magma cooling underground.
All minerals are rocks, and all rocks are minerals.
Show answer
Answer: False
Minerals and rocks are different. Minerals are naturally occurring inorganic solids with specific compositions. Rocks are made of one or more minerals, but a mineral is not a rock.
The scale used to measure a mineral's hardness is called the Mohs ________ scale.
Show answer
Answer: hardness
The Mohs hardness scale (1-10) measures a mineral's resistance to scratching. Talc is the softest (1) and diamond is the hardest (10). Harder minerals scratch softer ones.
Marble is a metamorphic rock that forms from which sedimentary rock?
1. Sandstone
2. Limestone
3. Shale
4. Granite
Show answer
Answer: Limestone
Marble is a metamorphic rock that forms when limestone is subjected to high heat and pressure. The calcite minerals in limestone recrystallize into the larger crystals found in marble.
The rock cycle shows that rocks can change from one type to another over geologic time.
Show answer
Answer: True
The rock cycle describes how rocks continuously transform over millions of years: igneous rocks can weather into sediment → sedimentary rock → buried deeper → metamorphic rock → melted → magma → new igneous rock.

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