Reference Tools for Igneous Rocks

What’s in This Toolbox?

Igneous Rock Identification Flowchart

Use this flowchart to guide you through deciding on a rock name. Note that this chart may include some rocks that are not assigned.

Go to the Igneous Rock ID Flowchart.

Mafic Colour Index (MCI) Chart

Use this diagram to help you estimate the percent of mafic (dark grey, black, and/or green) minerals.

Go to the MCI Chart.

Compositional Classification Diagram

A colour diagram showing the mineral breakdown of common igneous rocks, including photographs of the common types of rocks in each of the compositional categories (i.e., ultramafic, mafic, intermediate, felsic). Use this diagram to remind yourself about the different colours of igneous rocks, and the difference between phaneritic (coarse-grained) and aphanitic (fine-grained) textures.

Note: This diagram is from the textbook.

Go to the Compositional Classification Diagram.

Igneous Rock Identification Flowchart

Figure 3.10 | Flowchart for choosing an igneous rock name. Download the flowchart as a pdf file. Source: Saoirse MacKinnon (CC BY-NC-SA)

Mafic Colour Index (MCI) Chart

This diagram shows the percent of each circle covered by specs that represent minerals.  Dark minerals in a lighter background are shown on the left, and light minerals in a darker background are shown on the right. Note that the Light Minerals column is the negative of the Dark Minerals column, meaning that a coverage of 30% light minerals has 70% coverage of dark minerals.

FIgure 3.11 | Chart to aid in estimating the percent of a particular mineral in a rock. Download this chart as a PDF file. Source: Karla Panchuk (2020) CC BY-NC-SA. Modified after Shvetsov (1954) and Terry & Chilingar (1955).

Compositional Classification Diagram

Figure 3.12 | Classification diagram for igneous rocks. Igneous rocks are classified according to the relative abundances of minerals they contain. A given rock is represented by a vertical line in the diagram. In the mafic field, the arrows represent a rock containing 60% pyroxene and 40% olivine. The name an igneous rock gets depends not only on composition, but on whether it is intrusive or extrusive. Source: Karla Panchuk (2018) CC BY-NC-SA 4.0. Click for more attributions.

License

Icon for the Creative Commons Attribution-ShareAlike 4.0 International License

Laboratory Manual for Earth Science (2Ed) Copyright © 2024 by Karla Panchuk and Saoirse MacKinnon is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

Share This Book