Minecraft wiki entry for The_second_day, associated text: Sand and gravel have special uses: Sand is used for making glass, which is useful for windows and even transparent walls. However, note that glass is fragile — a creeper blast destroys any glass in the blast range. Glass also cannot be recovered once placed (without the appropriate enchanted tools); if mined or blown up, it does not drop anything. Gravel is used to produce flint, which is a key material needed to craft arrows. As a bonus, these can be crafted together with dye to form concrete powder, so any cactus or flowers you've picked up may come in handy.