Quartz
2 of the 6 encyclopedias on this shelf carry an entry for Quartz. Both are reproduced below, so you can see where they agree and where they differ.
The Encyclopedia of Founding (1892)
The purest condition of silicon is that of quartz, in which it forms hexagonal crystals terminated by six-sided summits. It is a very abundant and widely diffused mineral. Quartz rock is mainly composed of it, and it is in this substance that gold is more frequently found than in any other. Quartz is the principal constituent of nearly all granites, as well as the numerous sandstones, limestones, trap-rocks, etc. Sands of both desert and sea-shore, and the common flint, are chiefly composed of it; and many stones, as the agate, amethyst, carnelian, chalcedony, jasper, rock-crystal, etc., are simply varieties of quartz. It is thought that a great deal of the silica which exists in nature has been originally deposited in the soluble condition. The structure of the chalcedony, etc., proves that they were formed by a solution of silica having penetrated into a cavity in the surrounding rock and there crystallized. See throughout this work for a description of the substances mentioned.
Aiton's Encyclopedia (1910)
a mineral compound of silicon and oxygen. It is one of the most abundant rock materials, constituting large masses, as well as the sands of the desert and the seashore. Crushed it forms a beautiful sand. It enters into the make-up of granite, gneiss, quartzite, and sandstone. It is hard, scratching glass easily, and cannot be melted at ordinary temperatures or dissolved by ordinary acids. For this reason, glass, which is chiefly quartz, is valuable in a laboratory and in the household. Many varieties of pure quartz are colored, as rose quartz, the opal, the amethyst, the smoky quartz, chalcedony, sardonyx, agate, carnelian, onyx, and agatized wood. Pulverized quartz is frequently used in preference to sand, being clearer and purer, for making glass and porcelain. It is also used for making sandpaper, as the crushed particles have a fresher, sharper fracture than worn sand. The mineral known as pebble, used for spectacles, is a transparent quartz. See Sand ; Silicon
What Has Changed in the Last Century
Both accounts treat quartz purely as a rock-forming mineral and a raw material for glass, sandpaper and spectacle "pebbles" electric behaviour goes unmentioned, though the Curie brothers had found piezoelectricity in quartz in 1880. Within a few years of Aiton's 1910 entry that property became the mineral's most valuable use: Walter Cady built the first quartz crystal oscillator in the early 1920s, and quartz timekeeping went from laboratory clocks to the wristwatch with Seiko's Astron in 1969, while high-purity quartz sand is now the feedstock for the silicon of semiconductor chips. Most quartz used in electronics is no longer mined but grown hydrothermally as synthetic crystals. Two small corrections: limestone, which the 1892 writer lists among quartz-bearing rocks, is essentially calcium carbonate, and opal, which Aiton calls a variety of pure quartz, is amorphous hydrated silica rather than crystalline quartz.
Written for this edition, 2026.