Rocks turn into soil
Water and time change a rock in two ways.
A red crust on black rock
Basalt is a black rock that has iron in it. After a long time outside, a basalt rock can have a red layer on its surface.
Why does the black rock get a red layer?
What this lesson covers
The idea
Rocks also change chemically when water or chemicals in it react with them; these physical and chemical changes in rocks are together called weathering, which eventually leads to the formation of soil.
A red crust on black rock
Basalt is a black rock that has iron in it. After a long time outside, a basalt rock can have a red layer on its surface.
Why does the black rock get a red layer?
- Water or air with water vapour reacts with the iron in it
- Someone painted it red
- The Sun melts it red
Wait and watch
Switch on the physical changes, the chemical changes, or both. Then press Wait longer.
Two kinds of change, one result
Breaking into pieces is a physical change. The red layer of iron oxide is a chemical change: a new substance forms. Together they change the rock into soil.
Rocks also change chemically when water or chemicals in it react with them; these physical and chemical changes in rocks are together called weathering, which eventually leads to the formation of soil.
- Change in the rock | Kind of change
- It breaks into smaller pieces | Physical
- Black basalt gets a red layer of iron oxide | Chemical
Notes
Rocks break up (physical change) and also change chemically when water or chemicals in it react with them. These changes together are weathering, which eventually leads to the formation of soil.
Check yourself
Physical and chemical changes in rocks together are called …
Basalt gets a red layer when it stays in water or damp air for a long time. The red colour is due to …
The red layer on basalt is a chemical change because …
Weathering of rocks eventually leads to the formation of …
- erosion. Erosion is the moving of pebbles, soil and sediments from one place to another.
- weathering — correct. Yes!
- combustion. Combustion is burning. It is not the change of a rock by water and air.
- paint from the soil. No paint is involved. A new substance, iron oxide, forms on the rock.
- melted rock. The rock does not melt. Its iron reacts with water or air with water vapour.
- iron oxide — correct. Yes!
- a new substance forms — correct. Yes!
- the rock breaks into pieces. Breaking is a physical change. A red colour comes from a new substance.
- the rock becomes warmer. Warming is not what makes a chemical change. A new substance forms here.
- metal. Weathering makes soil, not metal.
- soil — correct. Yes!
- water. Water helps in weathering, but weathering does not make water.