How is chalcedony different from agate?

Chalcedony and agate are related in that agate is a specific variety of chalcedony. Chalcedony refers to a cryptocrystalline form of silica, composed of very fine intergrowths of the minerals quartz and moganite. It typically has a smooth, waxy luster and can be found in various colors.

Agate, on the other hand, is characterized by its unique banded appearance, displaying curved or angular layers that are typically formed from the deposition of silica in volcanic or metamorphic rocks. While all agate can be classified as chalcedony due to its composition, not all chalcedony displays the banding that defines agate. This hierarchical classification illustrates an important aspect of gemology where certain stones have broader category classifications, and understanding these relationships is crucial when identifying and categorizing colored stones.

The options that describe chalcedony as colorless or suggest differing formation processes do not accurately capture their relationship in mineralogy, which focuses on their structural similarities and variations. Thus, option C accurately reflects the category under which agate falls, emphasizing the connection between the two types of stones.