Rocks, minerals and crystals have distinctly different characteristics, but it can be hard to tell by just looking at them. Minerals are pure substances found naturally in the Earth. Examples of minerals include gold, diamond, quartz, pyrite and gypsum. Rocks are made up of minerals, but they also contain sediment or magma, depending on how they form. Examples of rock include granite, basalt, sandstone, marble and slate. Crystals are made up of atoms, molecules and ions that extend in all three dimensions, giving each crystal a unique shape. Crystals usually reflect light. Common crystals include sugar, salt, snowflakes and amethyst.
Comparing and contrasting the three substances can help kids understand the similarities and differences among them. Use a Venn diagram to easily compare and contrast two substances at the same time. To create a Venn, draw two overlapping circles on a large piece of paper. Label one side "Minerals" and the other "Rocks." Label the intersecting portion "Both." Talk with your children about characteristics and examples of each type of substance while jotting them down in the appropriate space on the diagram. Create another Venn to compare and contrast minerals and crystals or rocks and crystals.
Sorting a pile of rocks, crystals and minerals helps children see the differences firsthand. Allow your children to sort the rocks any way they want to at first. They might sort by size, color, shape or characteristics. Ask them to describe their reasons for sorting. After they have had an opportunity to sort the substances a few times, introduce one or two of the defining characteristics to help guide them to sorting into piles of rocks, minerals and crystals. Encourage them to write or draw about the sorting activity after it is finished to reinforce learning.
Activities that illustrate scientific concepts firsthand can help abstract ideas become more concrete for young learners. Show your children the difference between rocks and minerals with a simple clay or playdough activity. Using several different colors, ask them to form small chunks of clay into many balls. Talk about how each ball represents one pure mineral because it is only one color. Next, ask your children to combine two or more minerals into a bigger ball. Discuss how the minerals blend together to form a rock. As you encourage them to keep mixing the minerals, the colors will continue to blend, becoming duller. Discuss how rocks are often gray and brown because they are a mixture of minerals. Challenge your children to create many different kinds of rocks out of several minerals.