Earth Science Practice Test: Minerals and Rocks
- Minerals and Rocks
- 10 questions
- 15 minutes
This test covers how geologists identify minerals and how igneous, sedimentary and metamorphic rocks differ. Tip: hardness, streak, cleavage and luster are more reliable clues than color.
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Question 1
A geologist rubs a mineral across an unglazed porcelain plate and records the color of the line it leaves. Which property is she testing?
Correct answer: B
Streak is the color of a mineral's powder, made by rubbing it on a porcelain streak plate. It is often more reliable than the color of the whole sample, which impurities can change.
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Question 2
An unknown mineral scratches fluorite but is scratched by orthoclase feldspar. What is its approximate hardness on the Mohs scale?
Correct answer: D
Fluorite has a Mohs hardness of 4 and orthoclase has 6, so a mineral that scratches the first but not the second falls in between, at about 5.
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Question 3
Obsidian is volcanic glass that forms when lava cools in seconds. Why is obsidian not classified as a mineral?
Correct answer: A
A mineral must have an orderly, repeating crystal structure. Lava that cools too fast for crystals to form leaves glass, so obsidian is a rock-like solid but not a mineral.
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Question 4
When struck with a hammer, a sample of mica splits into thin, flat, smooth sheets. Which property does this show?
Correct answer: C
Cleavage is the tendency of a mineral to split along flat planes of weak bonding. Fracture is the opposite: breaking along rough or curved surfaces.
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Question 5
A sample of granite has crystals of quartz and feldspar large enough to see without a hand lens. What do the large crystals tell you about how the granite formed?
Correct answer: C
Large crystals need time to grow, so they form when magma cools slowly inside Earth. Lava that cools quickly at the surface makes small crystals or glass, as in basalt.
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Question 6
A sedimentary rock contains rounded pebbles cemented together in a finer matrix of sand. What is this rock called?
Correct answer: A
Conglomerate is made of rounded gravel-sized pieces that were worn smooth by moving water. Breccia also has large pieces, but they are sharp and angular.
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Question 7
A drop of dilute hydrochloric acid placed on a white rock bubbles strongly. Which mineral is most likely present in the rock?
Correct answer: B
Calcite (calcium carbonate) reacts with acid and releases carbon dioxide gas, which causes the fizzing. This is why limestone and marble bubble; quartz does not react.
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Question 8
Shale is buried deeply and exposed to moderate heat and pressure for a long time. Which rock does it most likely become?
Correct answer: D
Shale is a fine-grained mudrock, and low-grade metamorphism turns it into slate. Marble forms from limestone and quartzite from sandstone.
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Question 9
A mineral sample has a mass of 54 g and a volume of 20 cm3. What is its density?
Correct answer: A
Density is mass divided by volume: 54 g / 20 cm3 = 2.7 g/cm3. Dividing volume by mass gives 0.37, which has the formula upside down.
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Question 10
Which group of minerals makes up most of Earth's crust?
Correct answer: B
Oxygen and silicon are the two most abundant elements in the crust, so silicate minerals such as feldspar and quartz dominate it. Carbonates like calcite are common in limestone but are a small share overall.
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