Vesicular Igneous Rocks:
* Contain numerous holes or cavities (vesicles) within the rock.
* These vesicles are formed by gas bubbles trapped within the solidifying magma or lava.
* Usually have a frothy or spongy appearance.
* Examples: Pumice, Scoria, Vesicular Basalt.
Non-Vesicular Igneous Rocks:
* Lack vesicles.
* Solid and dense.
* Typically formed from magma or lava that cooled without significant gas content.
* Examples: Granite, Gabbro, Rhyolite, Diorite.
Here's a table summarizing the key differences:
| Feature | Vesicular Igneous Rocks | Non-Vesicular Igneous Rocks |
|---|---|---|
| Vesicles | Present | Absent |
| Appearance | Frothy, spongy | Solid, dense |
| Formation | Magma/lava with high gas content | Magma/lava with low gas content |
| Examples | Pumice, Scoria, Vesicular Basalt | Granite, Gabbro, Rhyolite, Diorite |
Why are vesicles formed?
As magma rises to the surface, the pressure decreases. This decrease in pressure allows dissolved gases in the magma to escape, forming bubbles. These bubbles are trapped within the cooling magma or lava, creating the vesicles we see in vesicular rocks.
Key Takeaway:
The presence or absence of vesicles is a key characteristic used to distinguish between vesicular and non-vesicular igneous rocks. This distinction helps geologists understand the conditions under which the rocks formed.
