Amethyst
3 of the 6 encyclopedias on this shelf carry an entry for Amethyst. All 3 are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a variety of quartz, stained a violet blue or purple by a trace of iron or manganese. It is a very handsome stone, much used for charms, seals, and rings, but is too common to be considered precious. It occurs in crystals in the interior of agate geodes, nodules, and other rock cavities. The finest specimens are obtained in India, Ceylon, Brazil, and Siberia. Very handsome amethysts are obtained on the shores of Lake Superior, deriving their stain from the Iron Range. Amethyst is a Greek word, signifying without intoxication, given from a popular belief that the wearer of an amethyst was in a measure exempt from danger of becoming intoxicated. The amethystine sapphire, a gem of great beauty and brilliancy, is often called the oriental amethyst. It is a variety of corundum.
Collier's New Encyclopedia (1921)
a variety of quartz. Its color is clear purple or bluish violet; hence it is sometimes called violetquartz. The coloring matter is generally believed to be manganese. The beauty and hardness of the amethyst cause it to be regarded as a precious stone. It occurs in veins or geodes in trappean and other rocks. The best specimens are brought from India, Armenia, and Arabia. The Oriental amethyst is a rare purple variety of sapphire. The last stone in the third row of the Jewish high-priest's breastplate was an amethyst (Exod. xxviii: 19); and the 12th foundation of the new Jerusalem, mentioned in Rev. xxi: 20, was to be an amethyst.
An Encyclopaedia of Occultism (1920)
This gem," says Camillus Leonardus, " is reckoned among the purple and transparent stones, mixed with a violet colour, emitting rosy sparkles." The Indian variety is the most precious. When made into drinking cups or bound on the navel, it prevented drunkenness. It is also held to sharpen the wit, turn away evil thoughts, and give a knowledge of the future in dreams. Drunk in a potion, it was thought to expel poison and render the barren fruitful. It was frequently engraved with the head of Bacchus, and was a favourite with the Roman ladies.
What Has Changed in the Last Century
Collier's said in 1921 that the colour "is generally believed to be manganese," and Aiton's in 1910 hedged between iron and manganese; both were wrong. Amethyst's purple is now known to come from traces of iron in the quartz lattice altered by natural radiation, which is why gentle heating turns much amethyst into yellow citrine or green prasiolite. The bigger shift is commercial: hydrothermally grown synthetic amethyst has been produced in quantity since the 1970s and is close to indistinguishable from natural stone without laboratory testing, so the gem is cheaper still than when Aiton's called it "too common to be considered precious." The old sources list — India, Ceylon, Armenia, Arabia — has largely given way to Brazil, Uruguay and Zambia, and the Lake Superior stones Aiton's praised remain a regional collector's specialty.
Written for this edition, 2026.