What characterizes a cryptocystalline structure?

A cryptocystalline structure is characterized by being composed of aggregates where the individual crystals are so small that they can only be observed under very high magnification. This means that, while the material is indeed crystalline in nature, the individual crystal units are not discernible to the naked eye. Instead, this structure blends a crystalline arrangement typical of minerals with characteristics of amorphous substances, resulting in a material where the crystal boundaries are not apparent.

This definition aligns closely with certain materials, such as chalcedony, which demonstrate a cryptocrystalline structure. In these stones, you can see the general properties of crystalline materials, but their minute crystal sizes prevent them from being classified as macrocrystalline. This fine granularity is what distinguishes them in the broader context of mineral classification.