The Three Rock Types — Practice · Grade 9 Science

Chapter: Rocks, Landscapes & Water

What this practice covers

By the end of The Three Rock Types you should be able to:

11 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: igneous rock, sedimentary rock, metamorphic rock, foliation.

Problem 1

A rock cooled quickly at Earth's surface and has tiny crystals you can barely see. What type of rock is this?
  1. Extrusive igneous rock
  2. Intrusive igneous rock
  3. Sedimentary rock
  4. Foliated metamorphic rock
Answer and explanation

Extrusive igneous rock

Fast cooling at the surface produces small or no crystals — that's extrusive (volcanic) igneous rock.

Problem 2

Which rock type forms from melted rock (magma or lava) that cools and hardens?
  1. Igneous
  2. Sedimentary
  3. Metamorphic
  4. Fossil
Answer and explanation

Igneous

Igneous rock forms when molten magma or lava cools and solidifies.

Problem 3

Slate splits along closely spaced, flat surfaces. Slate forms through metamorphism from which original rock?
  1. Granite
  2. Basalt
  3. Shale
  4. Limestone
Answer and explanation

Shale

Slate is a foliated metamorphic rock that forms when shale is subjected to heat and pressure.

Problem 4

Marble (from limestone) and quartzite (from sandstone) both form through metamorphism but show NO banding. What term describes this lack of banding?
  1. Foliated
  2. Non-foliated
  3. Extrusive
  4. Intrusive
Answer and explanation

Non-foliated

Non-foliated rocks lack a pervasive planar fabric. Mineral composition and growth conditions affect whether foliation develops.

Problem 5

A geologist estimates a limestone bed took 50,000 years to accumulate its 100 visible layers. On average, how many years does each layer represent?
Answer and explanation

500 years/layer

50,000 ÷ 100 = 500 years per layer.

Problem 6

Granite and gneiss can form from very similar starting minerals, yet granite has scattered crystals with no pattern while gneiss shows clear banding. Explain why they look so different.
Answer and explanation

Granite is an igneous rock that crystallized directly from slowly cooling magma, so its crystals grew in random orientations. Gneiss is a metamorphic rock formed when intense heat and pressure squeezed an existing rock hard enough to force its minerals to line up in parallel bands, creating foliation, without ever fully melting.

Problem 7

A sample has visible interlocking crystals and no bedding or fossils. Is the evidence enough for a unique rock name? Explain the reasoning in your own words.
Answer and explanation

No; it suggests possibilities but does not uniquely identify the rock.

The texture supports a crystalline origin but can occur in different rocks.

Composition and other features are still needed to distinguish alternatives.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 8

A lava sample cools rapidly and has tiny crystals. Why? Show the reasoning, not just the conclusion.
Hints

Texture supports an inference; composition and context strengthen identification.

Answer and explanation

Rapid cooling allows little time for crystal growth.

Problem 9

A foliated rock has aligned minerals but no evidence of melting. What origin fits?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Metamorphic alteration with differential stress is consistent with foliation; it is not proof of former liquid magma.

Problem 10

Metamorphic rocks can be foliated or nonfoliatedMetamorphic rocks can be foliated or nonfoliatedDirected-stress alignmentRecrystallized, not foliatedFoliation is an alignment/banding pattern; metamorphism can lack it.
Original qualitative metamorphic fabric models. The left isolates alignment under a selected stress geometry; the right illustrates a nonfoliated mosaic. The drawings do not identify exact mineral assemblages or set pressure/temperature values.
Interpret the supplied visual model. Can a rock without foliation still be metamorphic? Explain a suitable mechanism.
Answer and explanation

Yes. It can recrystallize in the solid state without a pronounced aligned fabric, depending on composition and conditions; marble is a common example.

Compare the aligned texture with the grain mosaic. The pressure arrows mark one simplified stress geometry, not complete three-dimensional forces.

Yes. It can recrystallize in the solid state without a pronounced aligned fabric, depending on composition and conditions; marble is a common example.

Response criteria

  • Read the labeled quantities, reference frame or objects correctly.
  • Explain the relation between the visual evidence and the mechanism.
  • Keep the drawing’s stated assumptions and limits in the conclusion.

Problem 11

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.

Browse all courses