E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A precious stone, consisting of half-transparent quartz: so called from Chalcedon, in Asia Minor, where it was first found. Its chief varieties are agate, carnelian, cats-eye, chrysoprase, flint, hornstone, onyx, plasma, and sard.
Albertus Magnus (book i. chap. 2) says: It dispels illusions and all vain imaginations. If hung about the neck as a charm, it is a defence against enemies, and keeps the body healthful and vigorous.