1. Name: __________________________ Date: ___________ Period:
________
Composition of Igneous Rocks
Directions: Using your knowledge of Earth Science and the Scheme for
Igneous Rock Identification chart on page 6 of your ESRT, answer the
following questions.
1. A sample of periodite was found to be 20% pyroxene, what percentage of the
rock is olivine?
2. A sample of granite was found to be 50% potassium feldspar, what percentage
of the rock is quartz, plagioclase feldspar, biotite, and amphibole.
3. A sample of rhyolite was found to be 15% amphibole, what percentage of the
rock is potassium feldspar, quartz, plagioclase feldspar, and biotite.
4. A sample of gabbro was found to be 15% plagioclase feldspar, what other
minerals are present and what percentage of the rocks composition do they
make up?