Geology: What Is A Vesicle ? - Name A Basic Igneous Rock .?

[HawaiiFishCave]

In Geology What Is A Basic Rock?


Thanks

[John S]

Basic, as opposed to acid (now felsic or silicic) was the original term for mafic rocks, apparently due to the fact that geologists of the time believed that basic rocks were formed in alkaline soils - hence base, and acid rocks were formed in acidic soils.

This has been shown to be false, but the terms are still used occasionally.

The basic or mafic igneous rocks are:
Basalt (fine-grained, cooled quickly so found in lava flows)
Dolerite (Medium grained, medium rate of cooling, generally found in shallow intrusions such as dykes)
Gabbro (Coarse grained, cooled slowly, generally in plutons deep underground)

The basic rocks are made mostly of ca-rich plagioclase feldspar and pyroxene with some olivine and occasionally small amounts of amphibole.

The silica content is roughly 40-55 % of weight SiO2.

Granite is a felsic or acidic rock.

A vesicle is a cavity formed by expanding gas during the cooling of an extrusive igneous rock. A good example of vesicles are those found in pumice.

If a vesicle is filled in by a secondary mineral it is described as an amygdale.