EARTH SCIENCE LAB Lab # _____

Igneous Rock Identification

Name:______Date:______Lab Day:_____Lab Period: ____

Part 1: Separate the igneous rock samples in your box into three groups based upon the following:

Group 1: Vesicular Igneous Rocks These rocks show evidence of gas pockets. These pockets may appear as small holes or bubbles in the rock. The rocks may feel lighter (less dense) due to the presence of the as pockets. The mineral crystals (grain size) in these samples are too small to be seen without a magnifying lens (less than 1 mm or non-crystalline).

Group 2: Polymineralic Rocks These rocks contain more than one mineral and are multi-colored. The mineral crystals(grain size) are large enough to be seen. (1mm – 10 mm).

Group 3: Monomineralic Rocks These rocks appear to be composed of only one mineral. The samples appear to be uniform. They are actually composed of several minerals with crystals too small to be seen (less than 1 mm or non-crystalline).

Part 2: Refer to page 6 of the Earth Science Reference Tables, “Scheme for Igneous Rock Identification” to help you identify the following rocks:

Sample A: This igneous rock is EXTRUSIVE (cooled quickly on the surface of the Earth during volcanic activity), has a non-crystalline grain size, and a glassy texture. It is of low to medium density, is primarily FELSIC in composition(contains Aluminum) and contains potassium feldspar, quartz, biotite and amphibole. This type of igneous rock usually appears black. What is the identity of this igneous rock?

Answer:______

Sample B: This sample of igneous rock is INTRUSIVE (cooled slowly inside the Earth from magma), has a grain size of 1mm to 10 mm, coarse texture, light color, and low density. The rock is primarily felsic in composition and contains potassium feldspar, quartz, plagioclase feldspar, biotite and amphibole. What is the identity of this igneous rock?

Answer:______

Sample C: This sample of igneous rock is extrusive with a grain size of less than 1 mm. It has a fine, vesicular texture(contains evidence of gas pockets or air bubbles), dark color, and high density. The sample is MAFIC in composition (contains iron and magnesium) and is composed primarily of plagioclase feldspar and pyroxene. It also contains small amounts of biotite, amphibole, and olivine. What is the identity of this igneous rock?