Rocks and Minerals — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
Limestone is an igneous rock that forms when a volcano erupts and lava cools quickly.
Corrected: Limestone is a sedimentary rock that forms when shells, coral, and other materials settle on the ocean floor and are compressed over time.
The corrected sentence is: "Limestone is a sedimentary rock that forms when shells, coral, and other materials settle on the ocean floor and are compressed over time.". The original sentence "Limestone is an igneous rock that forms when a volcano erupts and lava cools quickly." contained an error that needed to be fixed.
2. Fix the sentence:
The rock cycle ends when a rock becomes metamorphic because it cannot change again.
Corrected: The rock cycle never ends. A metamorphic rock can melt to form igneous rock or break down into sediment that becomes sedimentary rock.
The corrected sentence is: "The rock cycle never ends. A metamorphic rock can melt to form igneous rock or break down into sediment that becomes sedimentary rock.". The original sentence "The rock cycle ends when a rock becomes metamorphic because it cannot change again." contained an error that needed to be fixed.
3. Fix the sentence:
Minerals are identified only by their color because each mineral has a unique color.
Corrected: Minerals are identified by several properties including hardness, luster, streak, and color, because different minerals can share the same color.
The corrected sentence is: "Minerals are identified by several properties including hardness, luster, streak, and color, because different minerals can share the same color.". The original sentence "Minerals are identified only by their color because each mineral has a unique color." contained an error that needed to be fixed.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Melted rock below Earth's surface is called magma.
Magma is molten rock that exists below Earth's surface. When it reaches the surface, it is called lava.
2. Melted rock that reaches Earth's surface is called lava.
Lava is magma that has erupted onto Earth's surface through volcanoes or fissures.
3. The color of the powder a mineral leaves on a white tile is called its streak.
Streak is a reliable identification property because it is consistent for a mineral regardless of surface color variations.
4. The way a mineral reflects light is called its luster.
Luster describes how a mineral's surface interacts with light — metallic (shiny like metal) or non-metallic (glassy, silky, earthy, etc.).
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Describe how a sedimentary rock could become a metamorphic rock.
Sample answer: A sedimentary rock can be pushed deep underground by Earth movements. The intense heat and pressure at that depth change its structure and minerals, turning it into a metamorphic rock.
Burial → heat and pressure → metamorphism. Example: limestone (sedimentary) becomes marble (metamorphic).
2. Why do geologists use streak instead of just color to identify a mineral?
Sample answer: Many different minerals can look the same color, but the streak color is more reliable. For example, gold and pyrite both look golden, but gold leaves a yellow streak while pyrite leaves a black streak.
Surface color can vary due to impurities; streak color is a more consistent and reliable diagnostic property.