USGS Geology in the Parks
This glossary contains simplified definitions for technical terms used within this site.
For more complete, technical definitions, click
A normally dry stream bed that ocassionally fills with water.
Weathering includes two surface or near-surface processes that work in concert to decompose rocks. Both processes occur in place. No movement is involved in weathering. Chemical weathering involves a chemical change in at least some of the minerals within a rock. Mechanical weathering involves physically breaking rocks into fragments without changing the chemical make-up of the minerals within it. Mechanical weathering includes processes such as water in cracks freezing and expanding, or changes in temperature that expand and shrink individual minerals enough to break them apart.
Refers to a sedimentary deposit or rock with grains of the same approximate size.
A piece of foriegn rock enclosed within an igneous rock. The foriegn rock is
usually picked up from the walls surrounding the igneous rock and is frozen
in place before it has a chance to melt. (another term also used is inclusion)
Mineral of zirconium, silicon, and oxygen (zirconium silicate). Generally glassy-looking, microscopic, four-sided prisms. Most commonly formed in igneous rocks.