* Basalt:
* Dense and solid: Basalt is formed from cooled lava that is relatively rich in magnesium and iron. These elements are dense, resulting in a heavier rock.
* Low gas content: Basalt cools relatively quickly, and most of the trapped gases escape during the cooling process. This results in a solid, dense rock.
* Pumice:
* Porous and light: Pumice forms when lava with a high gas content erupts explosively. The rapid cooling traps the gas bubbles within the solidifying lava, creating a very porous structure.
* High gas content: The high gas content contributes to the low density and makes pumice so light that it can even float on water.
In essence: Basalt is heavier than pumice because basalt is a dense, solid rock with little air trapped within it, while pumice is a porous, airy rock filled with many gas bubbles.
