Which rocks break up fastest in freeze and thaw?
The question
Do permeable rocks lose more mass than impermeable ones when they are soaked and frozen again and again?
Water that soaks into cracks expands by about 9% when it freezes, prising rock apart. The same weathering breaks up meteorites that land in wet, cold places, which is one reason they survive best in dry deserts and Antarctica.
Equipment
- Small samples of chalk, sandstone, granite and slate
- A digital scale, plastic food bags and labels
- A freezer
- A tray and paper towels
Method
- Dry each rock, weigh it and label its bag.
- Soak the rocks in water for an hour, put each in its bag and freeze overnight.
- Thaw them, collect any loose crumbs in the bag, and repeat for 10 cycles.
- Finally, dry the rocks and weigh them again.
- What to measure
- Mass before and after, and the percentage of mass lost for each rock.
- How to present it
- A bar chart of percentage mass lost, with a link to how quickly meteorites weather in different climates.
- Take it further
- Find out how meteorite weathering grades are worked out and what they tell scientists about how long a meteorite has been on Earth.
Safety
Keep rock bags apart from food in the freezer, and wash hands after handling.