Silica and Sand Castles
If you want to see some real silica, go to the beach or to a playground with a sandbox. Beach sand (which is also what people put in sandboxes) is nearly all silica (actually molecules of silicon and oxygen). Notice how easy it is to get wet sand to stick together - that's the beginning of the formation of sandstone.
Look at sand through a magnifying glass to see how the little grains of sand look like glass - because glass is made out of sand (in fact, the magnifying glass itself is made from sand). Or, if you're at the beach and don't have a magnifying glass, use a good cellphone camera and zoom in on the sand. Take some sand home and look at it under a microscope. Is all the sand really rocks? These days, thanks to pollution, a lot of beach sand is actually tiny pieces of plastic, from plastic bags and bottles that were thrown away into the ocean and broke down into little tiny pieces.