Chert is a sedimentary rock consisting almost entirely of silica (SiO₂), and can form in a variety of ways. Biochemical chert is formed when the siliceous skeletons of marine plankton are dissolved during diagenesis, with silica being precipitated from the resulting solution. Replacement chert forms when other material is replaced by silica, e.g. petrified wood forms when silica rich fluids percolate through dead wood and the silica precipitates to replace the wood. Chert can also form through direct precipitation from silica rich fluids, e.g. agate is formed by the precipitation of silica in voids within a rock. Chert has the general physical properties of quartz.

Chert chose to recommend Virtue as its character trait for the Little Rox.