Rocks and Minerals — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. A hiker finds a rock with visible shell fossils pressed into it. What type of rock is it?
A) igneous
B) sedimentary
C) metamorphic
D) volcanic glass
Shell fossils are preserved when sediment buries them and hardens into rock. Only sedimentary rock forms gently enough to keep fossils intact; igneous and metamorphic processes would destroy them.
2. Which process would change granite into gneiss?
A) weathering and erosion
B) melting and rapid cooling
C) heat and pressure deep underground
D) compaction and cementation
Gneiss is a metamorphic rock. Granite changes into gneiss when it is buried deep underground and subjected to extreme heat and pressure that rearrange its minerals into bands.
3. Why does granite have larger crystals than basalt?
A) Granite contains different minerals
B) Granite cools slowly underground giving crystals more time to grow
C) Basalt forms deeper in the Earth where there is more pressure
D) Basalt contains more water which prevents crystal growth
Granite forms deep underground where magma cools very slowly, giving crystals plenty of time to grow large. Basalt cools quickly on the surface, so its crystals stay tiny.
4. A student rubs a mineral on a white tile and gets a red-brown powder. Which mineral property was tested?
A) hardness
B) luster
C) streak
D) cleavage
Streak is the color of a mineral's powder when rubbed on an unglazed tile. A red-brown streak on a white tile is a classic result for the mineral hematite.
Part B: Fill in the Blank
Write the correct answer on each line.
1. Conglomerate is a sedimentary rock made of rounded pebbles held together by natural cement.
Conglomerate forms when rounded pebbles and gravel are glued together by natural mineral cement, such as silica or calcite, that fills in the gaps between the pieces.
2. The Grand Canyon shows many layers of sedimentary rock built up over millions of years.
The Grand Canyon's colorful walls reveal hundreds of sedimentary rock layers, each deposited at a different time. The deepest layers are nearly two billion years old.
3. Fluorite has a hardness of 4 on the Mohs scale.
Fluorite sits at 4 on the Mohs scale, right between calcite (3) and apatite (5). A steel nail can scratch it, but a copper penny cannot.
4. When water seeps into rock cracks and freezes, it expands and causes physical weathering.
Freezing water expands inside rock cracks and pushes them apart. This is physical (mechanical) weathering because it breaks the rock without changing its chemical makeup.
5. Slate was once used to make school chalkboards because it splits into flat sheets.
Slate splits into smooth, flat sheets because of the way heat and pressure aligned its mineral grains. This made it perfect for old-fashioned chalkboards and roof tiles.