Emerald
3 of the 6 encyclopedias on this shelf carry an entry for Emerald. All 3 are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a precious stone. It is of a peculiar green color. It is found in the form usually of a short, six-sided crystal. It is rather a soft stone, being little harder than quartz. An emerald is composed chiefly of silicon and aluminum. It contains a trace of glucinum. Its color is due to oxide of chromium. When heated, the emerald turns blue, but resumes its natural color again when cool. If heated too far, however, it melts into a white, clouded mass of no value whatever. The emeralds of the ancients were obtained from Ethiopia and Upper Egypt. They were greatly prized, both on account of their rich color and the ease with which they could be carved into desired figures. The finest emeralds of modern times have been obtained from Peru, Colombia, and the Urals. The largest emerald known is that in the Royal Museum at St. Petersburg. It was obtained in the Ural Mountains and weighs over six pounds. A magnificent emerald gem is kept with the crown jewels in the treasure chamber of the imperial palace at Vienna. In the language of precious gems, the emerald represents success in love. Ireland is called the Emerald Isle because it is usually clothed with beautifully green vegetation.
An Encyclopaedia of Occultism (1920)
A good preservative against decay, promotes childbirth, arrests dysentery, and heals the bites of venomous animals. It is the most grateful of all jewels to the eyes, and reflects images like a looking-glass. Nero is said to have had one of immense size, in which he beheld the combats of the gladiators.
Collier's New Encyclopedia (1921)
a variety of beryl, distinguished from the latter by being emerald-green in place of pale green, light blue, yellow or white, the colors of the beryl. The finest emeralds are found in Peru, but they occur in various other places. In heraldry, the term designates the green tincture in coat-armor; vert.
What Has Changed in the Last Century
Collier's had the mineralogy right in 1921 e3Al3Al2Si6O18 Emerald is a chromium- (and sometimes vanadium-) coloured variety of beryl, and Aiton's "trace of glucinum" is simply beryllium under its older name. But the sourcing in both accounts is wrong in a way that has since been sorted out: Peru never had emerald mines, and the stones Spanish traders shipped from Lima came from Colombia, whose Muzo and Chivor deposits remain the benchmark for fine colour; since the 1970s Zambia's Kagem mine has become one of the largest producers by weight. The biggest change is that emeralds no longer have to be dug up at all e3Al3Al2Si6O18 Carroll Chatham grew commercially viable flux emeralds in the 1930s, and hydrothermal synthetics followed, while almost all natural stones on the market are routinely oil- or resin-filled to hide their fractures. The ancient Egyptian workings Aiton's mentions, in the Wadi Sikait area east of the Nile, have been systematically excavated by archaeologists in recent decades.
Written for this edition, 2026.