Road Map
A rock at Earth’s surface is broken into small pieces, carried downstream, deposited, buried, and eventually cemented together. What type of rock has formed?
Sedimentary rock
Layers of loose sand become buried. Pressure packs the grains together, and minerals deposited by water bind them. What overall process is occurring?
Lithification
A rock is changed by intense heat and pressure while remaining completely solid. What process has occurred?
Metamorphism
A student finds a rock made of visible grains cemented together. Which major rock type is the strongest initial classification?
Sedimentary rock
Sunlight travels through empty space before reaching Earth. Which method of energy transfer allows this to happen?
Radiation
A sedimentary rock is buried deep underground and exposed to intense heat and pressure, but it never melts. What type of rock could it become?
Metamorphic rock
A rock contains fragments of older rocks that were transported, deposited, compacted, and cemented together. How should this sedimentary rock be classified?
Clastic sedimentary rock
Minerals in a metamorphic rock become aligned into parallel layers because of directed pressure. What texture has developed?
Foliated texture
A rock contains mineral bands created when crystals realigned under pressure. Another rock contains layers made of deposited particles. Which one is metamorphic?
The rock with aligned mineral bands.
Two mineral samples look different in color but leave the same powdered color on a streak plate. Which property would be more reliable for comparing them?
Streak
A metamorphic rock melts deep underground and later cools and solidifies. What type of rock will result?
Igneous rock
A shallow body of water evaporates and leaves mineral crystals behind. Those crystals eventually form rock. What type of sedimentary rock is forming?
Chemical sedimentary rock
Marble contains interlocking crystals but no mineral bands. Would it be classified as foliated or nonfoliated?
Nonfoliated
A geologist finds a rock with crystals that formed as molten material cooled. What major rock type is it?
Igneous rock
Hot material in part of Earth’s mantle becomes less dense and rises while cooler, denser material sinks. Which energy-transfer process is occurring?
Convection
Students draw the rock cycle as a circle in which sedimentary rock must always become metamorphic rock next. What is wrong with their model?
The rock cycle does not follow one fixed sequence; rocks can follow many different pathways.
Two limestones contain the same mineral, calcite. One formed when calcite precipitated from water, while the other formed from accumulated shells. How should the two rocks be classified?
The first is chemical sedimentary rock; the second is organic sedimentary rock.
Sandstone next to a body of magma is heated strongly and changes into quartzite within a relatively narrow area. What type of metamorphism best explains this?
Contact metamorphism
Two rocks have similar colors, but one contains cemented grains while the other contains interlocking crystals. Why is texture more useful than color for identifying how these rocks formed?
Texture provides evidence about the rock’s formation process, while similar colors can occur in different rock types.
An unknown mineral scratches a mineral with a Mohs hardness of 4 but is scratched by one with a hardness of 6. What can you conclude about the unknown mineral’s hardness?
Its hardness is between 4 and 6 (approximately 5).
A rock is weathered and eroded into sediment, but the sediment never undergoes burial, compaction, or cementation. Why has a new sedimentary rock not formed yet?
The sediment has not undergone lithification.
A geologist finds sedimentary rock containing abundant shell fragments. What evidence about the rock’s formation does this provide?
Its sediment included material produced by living organisms, indicating an organic origin.
Geologists discover a huge region of foliated metamorphic rock where tectonic plates once collided. Which type of metamorphism most likely occurred, and what evidence supports that conclusion?
Regional metamorphism; tectonic forces produced high heat and directed pressure over a large area, producing foliation.
A scientist knows that a rock has changed significantly but finds evidence that it never melted. Why would classifying it as igneous be inconsistent with that evidence?
Igneous rock forms when molten rock cools and solidifies; a rock that changed without melting is consistent with metamorphism instead.
A rock deep underground is heated by Earth’s internal thermal energy, causing its minerals to recrystallize without the rock melting. Using ideas from both earlier lessons, explain what is happening.
Earth’s internal thermal energy is supplying energy to the rock, and the minerals are changing/recrystallizing while remaining solid, contributing to metamorphism.