Across

3. A form of calcium carbonate softer than marble but harder than chalk.
5. Where a river joins the sea.
7. Mass divided by volume.
9. A light grey volcanic rock that floats on water.
12. A flat deposit of rock.
14. Thousands of years.
17. Particle of rock like speck of sand.
20. Deposition (laying down) of small particles of rock, usually on a sea bed.
21. Shiny black, glassy volcanic rock. It has no crystals in it.
22. Things happening one after the other.

Down

1. Change state from liquid to solid.
2. Physical, biological or chemical breakdown of rocks.
4. Water in the solid state.
6. The concentration of an acid in a substance, often measured with universal indicator paper.
8. Black, volcanic rock with tiny crystals.
9. Ability to soak up liquid like a sponge.
10. A hard, white form of calcium carbonate that can be polished and that is used to make statues.
11. Liquid drops that fall from the sky in a storm.
13. Rubbing away, for example when rocks are swept along by a river.
15. The transport of weathered rock.
16. Hard, igneous rock with large pink, grey, black and white crystals.
18. When water changes state from solid ice to liquid water.
19. A chemical with a pH less than 7 that turns blue litmus paper red.