* Granite forms slowly deep underground: Granite crystallizes from magma (molten rock) that cools and solidifies slowly deep within the Earth's crust. This slow cooling allows mineral crystals to grow large, giving granite its characteristic coarse, interlocking texture. There's no opportunity for gas to escape and create air pockets.
* Pumice and Scoria form quickly at the surface: These rocks are formed from lava that erupts from volcanoes. The lava is full of dissolved gases that quickly expand as the lava cools and solidifies. This rapid cooling traps the expanding gases, creating the characteristic air pockets (vesicles) that give pumice and scoria their bubbly texture.
In short: The difference in air holes comes down to the speed of cooling and the presence of dissolved gases.
* Slow cooling, deep underground = no air holes (like granite)
* Fast cooling, full of gases = air holes (like pumice and scoria)
