Onyx
4 of the 6 encyclopedias on this shelf carry an entry for Onyx. All 4 are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
o'niks, a term applied to two quite different stones. The first is a variety of quartz, closely allied to agate. It varies in color from white to black, brown, or red. The ancients used this stone for many artistic purposes, especially for cameos. The second onyx is a variety of marble, called also oriental alabaster. It was known to the ancients. A celebrated quarry in Egypt was rediscovered in 1850. The world's choicest supply comes from Algeria. Mexican onyx of the sort first described has a recent reputation. Ancient Aztec quarries have been reopened. This onyx is used for clock cases, bureau and table tops, vases, and for many other ornamental articles. There are fallen forests of petrified trees in the southwestern part of the United States . Entire tree-trunks have been transformed into sections of chalcedony, agate, and onyx. One of the most famous of these is the petrified forest of Arizona.
Collier's New Encyclopedia (1921)
a semi-pellucid gem with variously colored zones or veins. Any stone exhibiting layers of two or more colors strongly contrasted is called an onyx, as banded jasper, chalcedony, etc., but more particularly the latter when it is marked with white and stratified with opaque and translucent lines. The ancients valued it very highly, and used it much for cameos, many of the finest cameos in existence being of onyx.
An Encyclopaedia of Occultism (1920)
Its properties resemble those of Jasper , besides which it increases saliva in boys, and is said to bring terrible shapes to the dreamer. If applied to the eye it acts as if it were alive, by creeping about and removing anything noxious.
The Encyclopedia of Founding (1892)
A chalcedony, with alternate layers of white, black, and brown. It is found in Saxony, Arabia, and Ireland, and is used largely for cameos. See PRECIOUS STONES.
What Has Changed in the Last Century
The mineralogy in these entries still holds: onyx is banded chalcedony, a cryptocrystalline quartz, and the confusion Aiton's flags in 1910 between that stone and "oriental alabaster" persists in the trade to this day "onyx marble," including the Mexican and Algerian material, is banded calcite, and gem trade rules now require it to be sold with a qualifier rather than as onyx alone. The one substantive change since 1892 is candour about treatment: the solid black onyx of jewellery is almost never natural but grey banded agate dyed with sugar and sulphuric acid, a process known in Idar-Oberstein in the nineteenth century and now near-universal, and disclosure of it is expected. Arizona's petrified forest, which Aiton's describes as fallen trunks turned to chalcedony and agate, was made a national monument in 1906 and a national park in 1962. The Occultism volume's claims of 1920 that onyx increases saliva in boys and brings terrible shapes to dreamers descend from medieval lapidaries and are read now as folklore, not as medicine.
Written for this edition, 2026.