ROCKS AND MINERALS
Look at Rock Crystals
Use a magnifying glass to observe both the size and shape of crystals in rocks.
Rub a gold ring on a piece of paper and it should not leave a mark. Now bite the gold and it should be soft enough to leave an impression.
Do the same with the fools gold.
You should find that fools gold (iron pyrites) is much harder than real gold, and leaves a black streak on the paper.