afelsitic

Afelsitic is a term used in geology to describe a type of volcanic rock that is rich in alkali feldspar, typically orthoclase or sanidine. These rocks are characterized by their light color, which ranges from pink to gray, and their fine-grained texture. Afelsitic rocks are often associated with explosive volcanic eruptions, where the rapid cooling of magma results in the formation of small, interlocking crystals.

The term "afelsitic" is derived from the Greek words "a-" meaning without, and "fels" meaning feldspar. This reflects the relative absence of quartz, which is a common component in other types of volcanic rocks like rhyolite. Afelsitic rocks are typically found in volcanic areas where the magma has a high alkali content, such as in continental rift zones or volcanic arcs.

Examples of afelsitic rocks include phonolite, a volcanic rock composed primarily of alkali feldspar and nepheline, and trachyte, a fine-grained volcanic rock with a similar mineral composition. These rocks are important in understanding the processes of magma generation and differentiation in volcanic systems.