1. Dissolved Gases: Basalt magma contains dissolved gases, primarily water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2). These gases are held in solution by the high pressure within the magma.
2. Ascent and Cooling: When magma rises towards the surface, the pressure decreases. This causes the dissolved gases to come out of solution and form bubbles within the magma.
3. Solidification: As the magma cools and solidifies, the bubbles become trapped within the rock. These trapped bubbles are what we call vesicles.
4. Shape and Size: The size and shape of the vesicles are determined by the rate of cooling, the viscosity of the magma, and the amount of dissolved gases.
In summary:
* Origin: Expansion of dissolved gases during cooling and solidification.
* Mechanism: Pressure decrease leads to gas exsolution and bubble formation.
* Trapping: Bubbles get trapped as magma cools and solidifies.
Vesicles are a common feature of basaltic rocks, and they can be found in a variety of shapes and sizes. They are often filled with secondary minerals, such as zeolites or calcite, formed by later alteration processes.
