Turquoise
2 of the 7 encyclopedias on this shelf carry an entry for Turquoise. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
tur-kois', a precious stone much used as a gem. It is composed chiefly of aluminium. The blue turquoise owes its color to the presence of a phosphate of copper. A trace of iron gives a greenish tint. It is found in veins. It is not a crystal. Large pieces are rare. The color fades on exposure to strong light. It is softer than the topaz--four points softer than the diamond. Turquoise was a favorite gem among the ancients. Fine specimens have been found in the mummy cases of Egypt,--no doubt from the peninsula of Sinai. The Bedouin Arab believes that the turquoise has power to dispel evil influences and to prevent bad dreams from coming true. Turquoise mines have been worked in Persia for centuries. The cut gems were imported into western Europe by way of Turkey, whence the name turquoise. The ancient Aztecs of Mexico had turquoise mines. The Mexican Indians still hold a tradition that the stone is sacred to Montezuma. The mineral is found also in New Mexico , Arizona, Nevada, and California. See Gem
Collier's New Encyclopedia (1921)
an amorphous us mineral occurring in reniform nodules and incrustations. Hardness, 6.0; sp. gr., 2.6- 2.83; luster, waxy to dull; color blue, bluish-green, apple-green; streak, white; rarely sub-translucent, mostly opaque. Composition: Phosphoric acid, 32.6; alumina, 46.9; water, 20.5-100, whence the formula, 2A12O2PO+5HO. Probably the Callais, Callaina, and Callaica of Pliny. A gem stone much used in ancient times in Persia, and in prehistoric times by the ancient Mexicans under the name of chalchihuitl. Originally found in Persia, where the best stones for jewelry purposes are still obtained, ed, through the locality of the Mexican chalchihuitl has lately been discovered.