Across

1. The transport of weathered rock.
5. Mass divided by volume.
6. When water changes state from solid ice to liquid water.
7. Black, volcanic rock with tiny crystals.
11. Rubbing away, for example when rocks are swept along by a river.
12. Water in the solid state.
14. A light grey volcanic rock that floats on water.
16. A chemical with a pH less than 7 that turns blue litmus paper red.
18. Particle of rock like speck of sand.
19. Contamination of the environment by humans.
20. Things happening one after the other.
21. The concentration of an acid in a substance, often measured with universal indicator paper.
22. A form of calcium carbonate softer than marble but harder than chalk.

Down

1. Where a river joins the sea.
2. Shiny black, glassy volcanic rock. It has no crystals in it.
3. Thousands of years.
4. A hard, white form of calcium carbonate that can be polished and that is used to make statues.
8. Physical, biological or chemical breakdown of rocks.
9. Liquid drops that fall from the sky in a storm.
10. A flat deposit of rock.
13. Regular arrangement of molecules. Diamonds, emeralds and rubies are examples.
14. Ability to soak up liquid like a sponge.
15. Hard, igneous rock with large pink, grey, black and white crystals.
17. Change state from liquid to solid.