Decorative gems have adorned watches for centuries. But, beyond diamonds and the classic trinity of rubies, emeralds and sapphires, a colorless variety of quartz called rock crystal actually is the stone used most often in horology.

Yet, “as a material, not a lot of people know about it,” said Tom Heap, deputy director and head of watch sales at Sotheby’s London. “But I think with the way we’re seeing watch brands operate nowadays, you’re seeing a return to low production and almost a kind of historical watchmaking. It’s like a painter looking back at the old masters.”

Van Cleef & Arpels and Chanel were among the brands to showcase new timepieces set with rock crystal at Watches and Wonders Geneva, the weeklong trade show ending Monday — creations that highlighted not only the brands’ stonecutting and setting know-how, but which also showed off the unusual features of this less familiar gemstone.

Formed of oxygen and silicon, two of the most abundant elements in the Earth’s crust, rock crystal takes its name from the ancient Greek word krustallos, meaning “frozen ice,” and has long been admired for its glass-like properties.

Some of the earliest examples of decorative rock crystal can be traced to ancient Mesopotamia, Egypt and Persia, where it was used in ornaments including vessels and figurines, according to Helen Molesworth, a gemologist and the senior curator of jewelry at the Victoria and Albert Museum in London.