Rocks and Minerals — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. Granite is commonly used for kitchen countertops because it is very hard.
Granite (igneous) is extremely hard and durable, making it resistant to scratching and ideal for countertops.
2. Limestone is used to make cement, a key ingredient in concrete.
Limestone is heated (calcined) to make quicklime, which is processed into Portland cement used in concrete.
3. Graphite, a soft mineral, is used in pencils to make the writing core.
Pencil 'lead' is actually a mixture of graphite (a soft mineral) and clay, not lead.
4. A mineral that can scratch glass has a hardness greater than 5 on the Mohs scale.
Glass has a hardness of about 5.5 on the Mohs scale. A mineral that scratches glass must be harder than 5.
5. Quartz is one of the most common minerals found in Earth's crust.
Quartz (silicon dioxide) is one of the most abundant minerals in Earth's continental crust.
6. The way a mineral breaks along flat surfaces is called cleavage.
Cleavage is the tendency of a mineral to break along specific flat planes determined by its crystal structure.
7. Hematite is an iron ore with a red streak even though it looks gray or black.
Hematite's streak is red-brown, which helped ancient peoples use it as a red pigment, despite its gray/black appearance.
8. Metamorphic rocks often have bands or layers of different minerals.
Heat and pressure cause minerals to recrystallize in parallel bands or layers — a texture called foliation.
9. Chalk is a soft sedimentary rock made from the shells of tiny sea creatures.
Chalk is a form of limestone made from the microscopic shells (calcite) of marine organisms called coccolithophores.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
hardness
→ how a mineral resists being scratched
how a mineral breaks along flat planes
streak
→ color of powder left on a tile
how a mineral resists being scratched
luster
→ how a mineral reflects light
color of powder left on a tile
cleavage
→ how a mineral breaks along flat planes
how a mineral reflects light
Hardness → resistance to scratching; streak → powder color on tile; luster → light reflection; cleavage → breaking along flat planes.