What the Ground Is Made Of · Page 1 of 2
You need: your eyes, and a wet finger
Wet a patch of it. Can you see separate grains or crystals, and are they bigger than a grain of sugar, smaller, or too small to see at all?
What it tells you. Grain size is set by how fast it cooled or how it was laid down. Big crystals mean it cooled slowly, deep underground. No visible grains at all usually means it cooled fast at the surface, or it was mud.
You need: your eyes, and the edge of the rock
Turn it and look at a broken edge, not the flat face. Are there stripes, bands or sheets running through it?
What it tells you. Layers mean it was laid down a bit at a time — sand, mud, shells, settling. Nothing that cooled from a melt has layers, so this one question rules out a whole kind.
What the Ground Is Made Of · Page 2 of 2
You need: a fingernail, a copper coin, a steel nail
Try to scratch the rock with each in turn, softest first. Note the first one that leaves a mark ON THE ROCK — check it is a scratch and not a streak of metal left behind.
What it tells you. Hardness is a property of the mineral, not the lump. It is the difference between chalk you can mark with a nail and quartz that will scratch the nail back.
You need: a drop of vinegar, and somewhere it is allowed
Put ONE drop on a fresh broken surface and watch closely. Fizzing may be tiny — put your ear to it.
What it tells you. Fizzing means carbonate, which means it was once shells and sea creatures. This is the fastest question on the sheet: it settles a third of the common rocks on its own.
Four answers usually name it. Take them to the key on sheet 11.