Emerald
3 of the 7 encyclopedias on this shelf carry an entry for Emerald. Both 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.