Molten thymol in the cold petri dish crystallized in 1 minute and looked like this enlarged view. Actual size of the crystals in mm is: 5 mm Molten thymol in the hot petri dish crystallized in 3 minutes and looked like this enlarged view. Actual size of the crystals in mm is: 5 mm
Two students are doing an experiment to find out if crystal size in igneous rocks can be related to the speed of cooling of a magma. They did not have equipment to melt rock, so they used thymol (C10H14O) to represent rock. Thymol melts easily at low temperature on a hot plate, and it cools and recrystallizes quickly. Thymol is a transparent, crystalline organic substance derived from the herb thyme and is used in antiseptics and disinfectants. Thymol gives off an odor that can irritate skin and eyes and cause headaches, but the EPA determined in 2009 that “thymol has minimal potential toxicity and poses minimal risk.” To be cautious, the students used a spoon to handle the thymol and did all of their work under a fume hood with supervision from their teacher. One of the students placed about 20 cm3 of thymol crystals in a small Pyrex beaker and melted it completely under a fume hood to model the formation of magma. The other student poured one-half of the molten thymol into a cold petri dish and the other half into a hot petri dish of the same size.
The results of the student’s experiment are shown in Fig. A5.2.1. Notice that the images are enlarged. Beside each image below, measure and record the actual size range of the crystals (in mm) that formed.
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