Because the rock is irregular in shape, you use the Displacement method to measure its volume.
After getting a cylindur (with measurements), you can it up half way with water.
For example: let say the cylindur is goes up to 10 cm. You will fill it up to 5 cm with water. Then when you put the rock inside, (for example), the water level goes up to 8 cm. You will then know that the rock that you put in displaces 3 cm of water
hope this helps
