Brittle vs. Ductile Rocks

15min Novice

A candy bar, made almost entirely from nougat, is a useful model for exploring how temperature affects a rock's response to stress. Together with their teacher, students compare the candy bar's response to stress to other materials explored previously (e.g. rubber bands and Marble Tongs). From this they see how different materials respond to the same stress. Building on this, students also explore how temperature can affect the deformation of the same material undergoing the same stress. The discussion at the conclusion of the demonstrations ties the concepts of deformation to faulting (earthquakes) and folding of rocks.


Students will be able to:

  • describe common examples of materials that exhibit brittle, ductile, and elastic deformation
  • correctly identify images of faults and folds
  • describe at least one way that the conditions of formation may have differed for faulted rock vs. folded rock

Related Videos

Video lecture on how temperature controls mechanical behavior of materials, including rocks. A Big Hunk candy bar is used as a model. The cold candy bar is brittle whereas the warm candy bar is ductile or "plastic".

Video Novice

Video lecture about elastic rebound and brittle material in the crust using a yardstick as a mechanical analog. This demonstrates elasticity, brittle fracture, and why it is difficult to predict earthquakes.

Video Novice

This demonstration shows that rocks are elastic by squeezing a slit core of rock.

Video Novice

Related Lessons

Through a demonstration lead by the teacher, the discrepant concept of rocks exhibiting elastic behavior is physically illustrated with an easily obtained, inexpensive model.

Lesson Novice

Using a block-and-sandpaper model, students collaborate in small groups to investigate how energy is stored elastically in rocks and released suddenly as an earthquake (the earthquake cycle). This activity emphasizes the role of mechanical models in understanding and testing ideas in science.

Lesson Novice

In this activity students will evalaute Silly Putty and Oobleck, both of which demonstrate proprieties of both solid and liquids, as a potential concrete model for Earth's Asthenosphere.

Lesson Novice

Related Animations

The Earth has 3 main layers based on chemical composition: crust, mantle, and core. Other layers are defined by physical characteristics due to pressure and temperature changes. This animation tells how the layers were discovered, what the layers are, and a bit about how the crust differs from the tectonic (lithospheric) plates, a distinction confused by many.

Animation Novice