Agate is micro- to crypto-crystalline quartz. The mineral name for agate is chalcedony (pronounced cal said kney). It can form through volcanic or sedimentary processes. Quartz is made up of silica and it tends to be hard and brittle so it tends to be glassy. It is also very abundant in nature and forms and endless variety of colors, patterns, and textures.
These properties make it a perfect lapidary material.
Jasper is a term used to distinguish the opaque agate and agate that's darker in colors such as browns, reds, mustard, black, and dark green. Jasper is also used to describe agate that is coarse grained.Terms like jasp-agate are used to describe agates that have both the properties of agate and jasper. This term is considered obsolete by most and is not used much anymore.
Utah has an abundance of agates and jaspers. Most of the Utah agate and jasper has it formations based in sedimentary rocks but there is also agate associated with volcanic activity such as Wendover agate. The formation of agate is extremely complex and not well understood by scientists. The variations and combinations are almost endless which makes it difficult to decipher how it forms. Notwithstanding, agate is common around the world and one of the most collected minerals there is. Because of the commonality it is often taken for granted and by many standards it is undervalued.The complexity of the bands and the other patterns and formations within the agate are dazzling and at the same time incomprehensible.