Cutting Glass Science Experiment

Introduce experiments to geology classes to add a hands-on element to the study of the earth.

The study of geology is the study of processes that take hundreds and thousands of years. It can be challenging for students to relate to this vast time frame. To get students engaged in the study of geology, use hands-on experiments that allow students to investigate with the properties of different rocks. One of the most commonly used ways to classify rocks is the Mohs Hardness Scale, which compares the relative hardness of rocks. From limestone to diamonds, rocks have remarkably different properties. Students can experiment with the hardness of rocks by observing which ones can scratch or cut glass.

Instructions

1. Dull window glass or magnifying glasses are thick enough for this experiment.

Get pieces of glass for each student. These pieces should be at least 3 inches by 3 inches and should have no sharp edges. Each student or group of students needs a piece of glass. The glass should be thick and difficult to break because the students will be exerting some pressure on it. Avoid the glass in picture frames, as it is likely to break under pressure.

2. Diamonds are considered to be a lasting treasure because they are very hard.

Go to a store that specializes in rock samples for collectors. Buy a selection of rocks that have different levels on the hardness scale. One is the softest on the scale, and 10 is the hardest. Talc is extremely soft and scores a 1 on the hardness scale. If you cannot find any talc at the store, graphite scores 1.5 and is found in a student’s pencil lead. Fluorite scores in the middle of the range, a 4 on the hardness scale. Quartz is easy to source and scores a 7. Glass scores a 5.5.

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3. A diamond saw blade can cut glass because diamonds are very tough.

Give the students a piece of glass and have them brainstorm ways to break, cut or score the glass. They may think of smashing it on the ground or breaking it with a hammer. Tell them that you would like them to create a scratch on the glass and have them brainstorm how they might do this. Commercial glass-cutting facilities use tools such as diamond saws to cut glass to size. They are using the hardness property of the diamond to cut the glass.

4. Have students observe what happens when each rock contacts the glass.

Have the students experiment with the different types of rocks. They may knock them on the glass or use them to scratch the glass. Have the students write down their observations about what happens when each rock contacts the piece of glass. From these experiments, have them determine which rocks are harder than glass and which ones are softer. At the end of the experiment, show the students Mohs hardness scale and have them rate the rocks on the hardness scale.