A silica mineral related to quartz. Superstition credits chalcedony
with magical and medicinal properties. It is a good specific
against fantasy and illusions of evil spirits. It supposedly
quickens the power of the body and renders its possessor fortunate
in law. To achieve the latter effect, it is to be perforated
and suspended by hairs from a donkey. The black variety is believed
to prevent hoarseness and clear the voice.