Academic Year 8

Year 8s look at the relationship between igneous rocks and crystal size.

While learning about the rock cycle, Year 8s have been looking at the earth’s crust and the igneous rocks that form through the cooling and solidification of magma.

Igneous rocks, they found out, contain crystals. Their size depends on how quickly the molten magma cools and hardens. The more slowly the magma cools, the bigger the crystals.

In a lab experiment, the girls carried out a number of tests to verify the scientific facts for themselves. First, they heated a crystalline solid called salol over a Bunsen burner until it formed into a white crystal not unlike magma.

They then observed it under a microscope while it was hot and repeated the process after it had been warmly gently and again when it had cooled. The process allowed the students to effectively examine three types of ‘igneous’ rocks.

Did they find that the crystals were larger if the salol cooled quickly or slowly? Could they come up with a simple rule to establish the relationship between the rate of cooling and crystal size?




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