Rocks and Minerals — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Which statement best explains why the rock cycle has no beginning or end?
A) Rocks only form one time and never change
B) Each rock type can be changed into any other rock type through natural processes
C) Only igneous rocks can start the cycle
D) Sedimentary rocks cannot become igneous rocks
The rock cycle is continuous because any rock type -- igneous, sedimentary, or metamorphic -- can be transformed into any other type through natural processes like melting, weathering, or heat and pressure.
2. A mineral scratches fluorite (hardness 4) but is scratched by quartz (hardness 7). What could its hardness be?
A) 2
B) 4
C) 5
D) 8
If the mystery mineral scratches fluorite (4) it must be harder than 4, and if quartz (7) scratches it, it must be softer than 7. A hardness of 5 fits between those two values.
3. Which type of rock would you most likely find near an active volcano?
A) sedimentary
B) metamorphic
C) igneous
D) fossil-bearing
Volcanoes produce lava, and when that lava cools and hardens it becomes igneous rock. That is why igneous rocks like basalt and obsidian are common near active volcanoes.
4. Why are fossils almost never found in igneous or metamorphic rocks?
A) These rocks are too soft to preserve fossils
B) Extreme heat or pressure destroys any fossils that may have been present
C) Only ocean animals leave fossils
D) Fossils only form in rocks younger than 100 years
Igneous rocks form from scorching magma or lava, and metamorphic rocks endure crushing pressure. Both processes would destroy any fossils, so fossils survive only in gently formed sedimentary rock.
Part B: Fill in the Blank
Write the correct answer on each line.
1. Pumice floats on water because it is full of trapped gas bubbles.
During a volcanic eruption, gas escapes from the lava and leaves tiny holes behind. These trapped gas bubbles make pumice so lightweight that it can actually float on water.
2. Calcite is a mineral that fizzes when you put acid on it.
Calcite reacts chemically with acid, producing carbon dioxide gas that appears as fizzing bubbles. Scientists use a drop of weak acid as a quick field test to identify calcite.
3. The oldest layers of sedimentary rock are found at the bottom of a rock formation.
Newer sediment always settles on top of older sediment, so the bottom layers were deposited first and are the oldest in any undisturbed rock formation.
4. Anthracite is a hard, shiny form of coal that burns very cleanly.
Anthracite is the highest grade of coal. Millions of years of heat and pressure transformed ancient plant material into this hard, shiny fuel that burns with very little smoke.
5. The Hawaiian Islands were formed by volcanic eruptions that built up layers of basalt over time.
The Hawaiian Islands sit over a volcanic hotspot. Repeated volcanic eruptions piled up layers of basalt lava on the ocean floor until the rock rose above the water's surface.