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:
Diamond is the softest mineral on the Mohs scale, with a hardness of 1.
Corrected: Diamond is the hardest mineral on the Mohs scale, with a hardness of 10. Talc is the softest mineral, with a hardness of 1.
The original had it backwards. Diamond is actually the hardest mineral at 10 on the Mohs scale, while talc is the softest at 1.
2. Fix the sentence:
Marble is a sedimentary rock that forms when sand grains pile up on a riverbed.
Corrected: Marble is a metamorphic rock that forms when limestone is changed by extreme heat and pressure inside the Earth.
Marble is metamorphic, not sedimentary. It forms when limestone gets transformed by intense heat and pressure deep inside the Earth.
3. Fix the sentence:
Erosion happens when rocks stay in one place and grow larger over time.
Corrected: Erosion happens when wind, water, or ice move pieces of rock and soil from one place to another.
Erosion is the movement of rock and soil from one place to another by wind, water, or ice. Rocks do not grow larger; they get worn down and carried away.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Sandstone is a sedimentary rock formed from tiny grains of sand cemented together.
Sandstone gets its name because it is literally made of sand grains that were pressed together and cemented over thousands of years.
2. Minerals that break along smooth, flat surfaces have a property called cleavage.
Cleavage means a mineral splits along smooth, flat planes because of the orderly way its atoms are arranged inside.
3. Granite contains visible crystals of quartz, feldspar, and mica.
Granite's three main minerals are quartz, feldspar, and mica. You can often spot the shiny, flaky mica flakes when you look closely at a piece of granite.
4. Rocks that form from cooled lava on Earth's surface have small crystals because they cool quickly.
When lava cools quickly on the surface, mineral crystals do not have enough time to grow large, so the rock ends up with very small crystals.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Name two ways people use rocks or minerals in everyday life.
Sample answer: Granite is used for kitchen countertops and building stones because it is hard and durable. Graphite, a soft mineral, is used inside pencils for writing.
Rocks and minerals have many everyday uses. For example, granite's hardness makes it great for countertops and buildings, while graphite is soft enough to leave marks, which is why it goes inside pencils.
2. How can an igneous rock become a sedimentary rock?
Sample answer: An igneous rock is broken into small pieces by weathering. Wind and water carry those pieces, called sediment, to a lake or ocean where they settle in layers. Over time, the layers are pressed and cemented together to form sedimentary rock.
The rock cycle connects all rock types. An igneous rock gets broken down by weathering, carried away by erosion, and deposited as sediment that is eventually pressed and cemented into sedimentary rock.