Mohs Ladder Game

The Mohs scale ranks minerals by hardness: which one can scratch which. Its ten rungs run from talc at 1 to diamond at 10, and a harder mineral always scratches a softer one. In this game you build the scale from memory, rung by rung, and then use it in scratch duels, where the ladder hides its names and you have to know which of two minerals is harder.

How to play

1. Build the ladder. The ten minerals come one at a time in a shuffled order. Tap the rung each one goes on, or press its number, with 0 for rung 10.
2. A mineral on the wrong rung costs a life, and goes on its own rung, so you see where it belongs.
3. Scratch duels. Two minerals meet, and the ladder hides its names. Pick the one that scratches the other: the one on the higher rung. Both rungs light up with their names once you answer.
4. After eight duels the field kit joins: a fingernail, a copper coin, glass and a steel knife, with their hardness beside the ladder.
5. Three lives lost end the game.

On a keyboard, press 1 or the up arrow for the upper card in a duel, and 2 or the down arrow for the lower one. Space or Escape pauses.

Scoring

• Each mineral put on its rung scores 50 points.
• A ladder built with no mistakes scores 250 points more.
• A duel won scores 100 points, plus 20 for each duel already won in a row, up to 200 a duel.
• Practice takes no lives and saves no scores, so you can learn the ladder at your own pace.

Your five best scores are saved in this browser only.

The ten rungs

The German mineralogist Friedrich Mohs chose ten well-known minerals and put them in order of which scratches which:

1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Orthoclase
7. Quartz
8. Topaz
9. Corundum
10. Diamond

The scale only puts them in order. It does not measure how much harder one is than the next, and the gap between corundum and diamond is far larger than any other step. Each mineral is drawn in its common crystal shape, but the game never asks about colour, since many minerals come in several.

The everyday markers

Geologists test hardness in the field with things they carry. Sources give their hardness only roughly, and the objects themselves vary, so the game gives each one as about: a fingernail about 2.5, a copper coin about 3.5, glass about 5.5 and a steel knife about 5.5 to 6.5. A marker only meets a mineral at least a whole step away from everything the sources give for it, so the game never asks about a close call such as a fingernail on gypsum or a coin on calcite.

To remember the ten in order, give each rung a peg from a peg list. With the Major System, rung 7 is a cow, so a cow carved from quartz holds the fact.

For more lists worth learning, see our trivia lists to memorize, or try our other free memory games.