Question Name____________________________________________________Section________________Date___________ Week 4: Exploring Earth – Igneous Rocks and Coordinate Systems

Name____________________________________________________Section________________Date___________

Week 4: Exploring Earth – Igneous Rocks and Coordinate Systems

Invitation to Inquiry

Survey the use of rocks used in building construction in your community. Compare the type of rocks that are used for building interiors and those that are used for building exteriors. Are any trends apparent for buildings constructed in the past and those built in more recent times? If so, are there reasons (cost, shipping, other limitations) underlying a trend or is it simply a matter of style?

Part 1: Rocks on Earth

Background

Igneous rocksare rocks that form from the cooling of a hot, molten mass of rock material.Igneous rocks, as other rocks, are made up of various combinations of minerals. Each mineral has its own temperature range at which it begins to crystallize, forming a solid material. Minerals that are rich in iron and magnesium tend to crystallize at high temperatures. Minerals that are rich in silicon and poor in iron and magnesium tend to crystallize at lower temperatures. Thus, minerals rich in iron and magnesium crystallize first in a deep molten mass of rock material, sinking to the bottom. The minerals that crystallize later will become progressively richer in silicon as more and more iron and magnesium are removed from the melt.

Igneous rocks that are rich in silicon and poor in iron and magnesium are comparatively light in density and color. The most common igneous rock of this type is granite, which makes up most of the earth’s continents. Igneous rocks that are rich in iron and magnesium are dark in color and have a relatively high density. The most common example of these dark-colored, more dense rocks is basalt, which makes up the ocean basins and much of the earth’s interior. Basalt is also found on theearth’s surface as a result of volcanic activity. Other common igneous rocks are obsidian, pumice and gabbro that you will investigate through the lab.

Procedure

1. For this experiment you can chose to either measure 5 different rocks (options given by your instructor – likely basalt, granite, obsidian, pumice and gabbro) or 5 different specimen of the same rock. Decide with your lab partners which you’d like to do.

2. Use a balance to find the mass of your first rock. Record the mass in Data Table 4.1. Tie a 20-cm length of nylon string around the rock so you can lift it with the string. Test your tying abilities to make sure you can lift the rock by lifting the string without the rock falling.

3. Place an overflow can on a ring stand, adjusted so the overflow spout is directly over a graduated cylinder.

4. Hold a finger over the overflow spout, then fill the can with water. Remove your finger from the spout, allowing the excess water to flow into the cylinder. Dump this water from the cylinder, then place it back under the overflow spout.

5. Grasp the free end of the string tied around the first rock, then lower the rock completely beneath the water surface in the overflow can. The volume of water that flows into the graduated cylinder is the volume of the rock. Remembering that a volume of 1.0 mL is equivalent to a volume of 1.0 cm³, record the volume of the rock in cm³ in Data Table 4.1.

6. Calculate the mass density of this first rock and record the value in the data table.

7. Repeat procedure steps 1 through 5 with 4 more rocks.

Results

1. In what ways do igneous rocks have different properties?

2. Explain the theoretical process or processes responsible for producing the different properties of igneous rock

3. According to the experimental evidence of this investigation, propose an explanation for the observation that the bulk of the earth’s continents are granite, and that basalt is mostly found in the earth’s interior.

4. Was the purpose of this lab accomplished? Why or why not? (Your answer to this question should show thoughtful analysis and careful, thorough thinking.)

Part 2: Coordinate systems on Earth

Background

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