Geology and Minerals
Argillic is a term used in the United States Department of Agriculture Soil taxonomy to describe a subsurface horizon categorized by clay-enrichment. It is analogous to the Argic horizon in the World Reference Base system of soil taxonomy used outside of the United States. The term "Argillic" comes from the Latin argilla, meaning clay. The term Argic used by the WRB system also comes from this same root. Clay accumulation occurs in the mineral soil through primarily illuviation and translocation of preexisting clays with some formation in-situ in the soil. The red color is caused by the formation of iron oxides which form under the same wet conditions as the clay accumulation occurs.
List of Quaternary volcanic eruptions.
Geology.
Text from Wikipedia; plate via Wikimedia Commons. Text CC BY-SA 4.0; plate freely licensed (see Commons). Source record. Images and catalogue data are reproduced from open-access collections.