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Igneous Rocks Model

David Steer (steer@uakron.edu) and Kyle Gray (krg10@uakron.edu), University of Akron
This material is based upon work supported by the National Science Foundation under Grant No. GEO-0506518.

This activity was selected for the On the Cutting Edge Reviewed Teaching Collection

This activity has received positive reviews in a peer review process involving five review categories. The five categories included in the process are

  • Scientific Accuracy
  • Alignment of Learning Goals, Activities, and Assessments
  • Pedagogic Effectiveness
  • Robustness (usability and dependability of all components)
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This page first made public: Aug 25, 2008


While working in groups to facilitate peer tutoring, students use samples of four igneous rocks (gabbro, basalt, granite, and rhyolite) to observe differences in texture, color and grain size and make inferences about the relative cooling histories and silica content associated with each magma type.

Learning Goals

Students will:

Context for Use

This model works well during units on the properties and formation of igneous rocks, as well as surveys of the different rock types or factors that influence the explosivity of a volcanic eruption. Students work in groups of 2-4 individuals as they make observations and predictions and the students are allowed to use the rock identification chart in their texts.

Teaching Materials

Igneous Rocks
Each student model consists of the following material:
Four rock samples, including pieces of

Samples should be uniform both within and between specimens. The rhyolite and basalt samples should contain few phenocrysts. All rocks should be clearly identified (e.g. samples 1-4), and all sample sets should have the same identification scheme (i.e. all granites are #1). Samples used in this exercise were purchased from a scientific supply company.

Teaching Notes and Tips

Students are provided the four samples and instructed to find similarities and differences between the samples. Students typically note mineral sizes and color differences. Processes associated with plutonic and volcanic rocks are discussed. Students identify the texture (fine-grained vs coarse-grained) of each rock sample and use their observations to identify the volcanic and plutonic rocks and discuss cooling histories of the rocks.

Students sort rocks with similar texture rocks in rows and similar color rocks in columns. Connections between silica content and bulk rock color are discussed. Students sort the rocks based on their silica content (gabbro and basalt vs granite and rhyolite) and label each rock. The instructor assesses student understanding by asking which rocks belong to the high (or low) silica category. Higher-order processing skills can be enhanced by asking which rocks represent magma that would produce a more (or less) explosive eruption if magma viscosity has been discussed.

Students name each rock type by using the texture and color of each rock sample.

Caution: It may be difficult to find samples of gabbro that do not look like the basalt. Also, the actual samples may vary in color and texture from the photos shown in class or in the textbook.


Several different assessment techniques can be used depending on time and the needs of your class.

References and Resources

Archived ConcepTest questions used with this model:


Geoscience:Geology:Igneous and Metamorphic Petrology:Igneous Rocks

Resource Type

Activities, Classroom Activity:Short Activity:Demonstration

Grade Level

College Lower (13-14), Introductory Level, High School (9-12)

Earth System Topics

Solid Earth:Earth Materials:Rocks


Solid Earth:Petrology:Igneous Rocks


Teach the Earth:Teaching Environments:Intro Geoscience, Teach the Earth:Course Topics:Petrology

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