✍️Activity 7A: The Mafic Color Index (MCI)

For this activity, you will need igneous rock samples selected by your instructor. Locate these samples before you begin.

Take a close look at the rocks; how are they different? When you hold them closer to a light source, do you notice if they reflect light? Are they dull looking? Have small shiny surfaces? Are they extremely shiny and smooth? Have holes?

Separate the samples into three groups based on their color (dark, light or intermediate), as a first attempt at classifying rock compositions based on color.

Then, answer the following questions. Hint: You may need to examine the additional photos provided in the Igneous Rock Index to see the different minerals clearly.