Rocks, Landscapes & Water — Problem set, Grade 9

Identify Earth materials and explain how rock, water, and surface processes shape landscapes.

Review the key ideas

Minerals & Their Properties

Minerals are identified by testable properties — streak, luster, and hardness are far more reliable than color alone.

The Rock Cycle

The rock cycle has no beginning or end — cooling, weathering/erosion, lithification, metamorphism, and melting constantly recycle rock among all three rock types.

The Three Rock Types

Use composition, texture, and context together. Igneous rocks crystallize from melt; sedimentary rocks form from sediment or precipitation; metamorphic rocks change without bulk melting.

Weathering, Erosion & Deposition

Weathering breaks rock down in place, erosion carries the pieces away, and deposition drops them somewhere new once the carrying agent loses energy.

Groundwater, Watersheds & Water Budgets

Storage changes when water inputs and outputs differ; pore connectivity affects how water moves.

Problem 1

What is the Mohs hardness of talc, the softest of the ten reference minerals?
Answer and explanation

1

Talc sits at the very bottom of the Mohs hardness scale, with a hardness of 1 — it can be scratched by a fingernail.

Problem 2

Two mineral samples both look shiny silvery-gray, but Sample A leaves a black streak and Sample B leaves a reddish-brown streak on a porcelain plate. Are they the same mineral? Explain.
Answer and explanation

No — they are different minerals.

Color and outward appearance can be misleading, but streak is much more reliable since it isn't affected by surface tarnish. Two different streak colors mean two different minerals (for example, galena streaks gray-black while hematite streaks reddish-brown).

Problem 3

A mineral scratches calcite (hardness 3) but does NOT scratch fluorite (hardness 4). What is the possible range of its Mohs hardness?
Answer and explanation

Greater than 3, and at most 4 (3 < hardness ≤ 4)

Scratching calcite means the mineral's hardness is greater than 3. Failing to scratch fluorite means its hardness is not greater than 4. Combining both clues gives a hardness greater than 3 and at most 4.

Problem 4

What do geologists call magma once it erupts above Earth's surface?
Answer and explanation

Lava

Molten rock is called magma while it's below the surface; the same material is called lava once it erupts above the surface.

Problem 5

What process changes an existing rock's minerals or structure using heat and/or pressure, without ever fully melting it?
Answer and explanation

Metamorphism

Metamorphism transforms an existing rock into metamorphic rock through heat and/or pressure alone, without the rock ever fully melting into magma.

Problem 6

Trace a path through the rock cycle that starts with igneous rock and ends as metamorphic rock, without ever melting again along the way. Name every process involved, in order.
Answer and explanation

Igneous rock → weathering and erosion → sediment → lithification → sedimentary rock → heat and pressure (metamorphism) → metamorphic rock

First, weathering and erosion break the igneous rock down into loose sediment. Next, lithification (compaction plus cementation) turns that sediment into sedimentary rock. Finally, heat and pressure metamorphose the sedimentary rock into metamorphic rock — all without the material ever melting into magma.

Problem 7

A rock has large interlocking crystals with no layering. Is this sufficient to identify it as igneous? Explain.
Answer and explanation

No. Metamorphic and some sedimentary rocks can also be crystalline.

Use mineral composition, texture, and field relationships together. Crystals and lack of layering alone do not establish origin.

Problem 8

Explain the key difference between how intrusive and extrusive igneous rocks cool, and how that difference affects their crystal size.
Answer and explanation

Intrusive rock cools slowly underground, forming large crystals; extrusive rock cools quickly at the surface, forming small or no crystals.

Slow cooling underground gives atoms time to arrange into large, visible crystals, producing coarse-grained intrusive (plutonic) rock like granite. Fast cooling at Earth's surface leaves little time for crystals to grow, producing fine-grained or glassy extrusive (volcanic) rock like basalt or obsidian.

Problem 9

Marble (formed from limestone) shows no banding, while gneiss shows strong, wavy banding. Both are metamorphic rocks. Using the term foliation, explain why they look so different.
Answer and explanation

Marble typically lacks foliation; gneiss commonly has compositional banding. Mineral composition and deformation conditions influence these textures.

Foliation is a planar fabric, which can include aligned minerals, cleavage, or compositional bands. It is not always visible banding. Calcite-rich marble commonly has a non-foliated texture; gneiss has a banded fabric.

Problem 10

What term describes the small, loose pieces of rock, mineral, or organic material produced by weathering?
Answer and explanation

Sediment

Weathering breaks rock down into small, loose pieces called sediment, which can then be transported by erosion.

Problem 11

Classify each as physical (mechanical) or chemical weathering: (a) water freezes inside a crack and splits the rock apart; (b) acidic rainwater slowly dissolves a limestone surface.
Answer and explanation

(a) Physical (mechanical) weathering; (b) Chemical weathering

Frost wedging (a) changes only the rock's size and shape without changing what it's made of, so it's physical weathering. Dissolving limestone (b) actually changes the rock's chemical composition, so it's chemical weathering.

Problem 12

A river carrying sand and gravel flows into a calm lake and builds a fan-shaped landform right at its mouth. Name the landform and the process that built it, and explain why it forms specifically at that location.
Answer and explanation

A delta, built by deposition, forming where the river suddenly loses energy entering the calm lake.

As the fast-flowing river enters the calm lake, it slows down sharply and loses the energy it needs to keep carrying its sediment load. That sediment is dropped right where the river meets the lake, building up into a fan-shaped landform called a delta.

Problem 13

Mineral A scratches mineral B, and B scratches C. The hardest is
  1. A
  2. B
  3. C
  4. cannot tell
Answer and explanation

A

Scratching indicates greater hardness, so A > B > C.

Problem 14

Two samples look identical but one has a white streak and one a reddish-brown streak. What can you conclude?
Answer and explanation

They are different minerals, despite the similar appearance. Streak reflects the colour of the powdered mineral and is far less affected by impurities or surface weathering than the bulk colour, so a clear difference in streak is strong evidence of different composition. Confirming it would mean checking hardness and density as well.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 15

Chapter review: A specimen has mass 54 g and displaces water from 20 to 38 mL when fully immersed without bubbles. Find its density and explain what additional evidence is needed to identify its mineral.
Answer and explanation

Volume is 18 mL = 18 cm³, so density is 54/18 = 3 g/cm³. Use hardness, streak, cleavage and other characteristic observations; density alone may match several candidates.

Find displaced volume: 38−20 = 18 cm³.

Calculate density: 54/18 = 3 g/cm³.

Compare several tests and uncertainty rather than naming a mineral from one value.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 16

A rock is melted and then cools underground. The result is
  1. sedimentary
  2. metamorphic
  3. intrusive igneous
  4. unchanged
Answer and explanation

intrusive igneous

Cooling below the surface gives intrusive igneous rock with larger crystals.

Problem 17

Explain why the rock cycle means Earth's oldest surface rocks are far younger than Earth itself.
Answer and explanation

Surface rock is continually destroyed and remade: weathering breaks it down, subduction consumes ocean floor, and heat and pressure reset metamorphic and igneous rock. Earth is about 4.5 billion years old, but most rock at the surface has been recycled since then, so only a few unusually protected areas preserve rock approaching that age.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 18

Chapter review: A rock contains sand grains cemented together. A student calls cementation the same as cooling molten sand. Distinguish the two pathways and name an observation that could help test the interpretation.
Answer and explanation

Cementation binds deposited grains through mineral precipitation; cooling a melt forms igneous material. Preserved grain boundaries, sedimentary textures and field relationships help test a cemented-sediment interpretation. Melting is not required for sandstone.

Cementation binds deposited grains through mineral precipitation; cooling a melt forms igneous material. Preserved grain boundaries, sedimentary textures and field relationships help test a cemented-sediment interpretation. Melting is not required for sandstone.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 19

Large crystals in an igneous rock indicate that the magma cooled
  1. quickly at the surface
  2. slowly underground
  3. in water
  4. without minerals
Answer and explanation

slowly underground

Slow cooling gives crystals time to grow large; rapid surface cooling gives fine grains or glass.

Problem 20

A rock shows distinct parallel bands of minerals. State the type and what the banding records.
Answer and explanation

It is metamorphic, and the banding — foliation — records directed pressure that aligned the mineral grains perpendicular to the squeezing. The bands therefore preserve not just that the rock was altered but the direction of the forces that altered it, which is information the original rock did not carry.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 21

Chapter review: A specimen has interlocking crystals but no foliation. Is it necessarily igneous? Explain two possible histories and the evidence that would help distinguish them.
Answer and explanation

No. Cooling a melt can yield an igneous crystalline rock, while solid-state recrystallization can yield a nonfoliated metamorphic rock. Mineral composition, texture details, contacts and field relationships help distinguish the histories.

No. Cooling a melt can yield an igneous crystalline rock, while solid-state recrystallization can yield a nonfoliated metamorphic rock. Mineral composition, texture details, contacts and field relationships help distinguish the histories.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 22

Rounded pebbles in a river bed indicate
  1. no transport
  2. transport over distance with repeated collisions
  3. chemical dissolution only
  4. volcanic origin
Answer and explanation

transport over distance with repeated collisions

Edges are knocked off during transport, so roundness increases with distance travelled.

Problem 23

Explain how plant roots contribute to both physical and chemical weathering.
Answer and explanation

Roots grow into cracks and widen them as they thicken, breaking the rock apart physically. They also release acids and support microbial activity that chemically attacks minerals at the root surface. The two effects work together: widened cracks admit more water and air, which accelerates the chemical attack.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 24

Chapter review: Trial A produces 12 g of sediment in 120 mL runoff; trial B 9 g in 60 mL. Compare total sediment export and concentration, then name two conditions to control when testing a surface cover.
Answer and explanation

B exports less mass (9 vs 12 g) but greater concentration (0.15 vs 0.10 g/mL). Control rain input, slope, material and collection interval, except for the planned cover change.

Calculate A: 12/120 = 0.10 g/mL.

Calculate B: 9/60 = 0.15 g/mL.

Distinguish total export from concentration and match test conditions.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 25

A town plans to double well withdrawals because groundwater is renewable. Evaluate that reasoning.
Answer and explanation

Compare recharge, natural outflow, current storage trends, and effects on streams or other users. Renewable supply can still be depleted when outputs exceed inputs.

Problem 26

Chapter review: A catchment begins with 300 m³ of stored water. Over one month it receives 100 m³ and loses 70 m³ by outflow/evapotranspiration plus 45 m³ by withdrawal. Find storage change and final storage. Explain why high porosity alone would not guarantee fast recharge.
Answer and explanation

Storage change is 100−70−45 = −15 m³ and final storage is 285 m³. Transmission also depends on connected pathways, permeability, gradients and conditions; porosity alone is a storage fraction.

Combine outputs: 70+45 = 115 m³.

Change is −15 m³; add to initial 300 m³ to get 285 m³.

Distinguish pore-space amount from connected transmission.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.
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