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Some people think that chalcedony is also a gem for June as well as pearl and moonstone. In general, chalcedony is a cryptocrystalline form of silica. Chalcedony has a waxy luster, and may be semitransparent or translucent. It can assume a wide range of colors, but those most commonly seen are white to gray, grayish-blue or a shade of brown ranging from pale to nearly black. The mineral gets its name from the town of Chalkedon, an ancient town in Asia Minor.

Chalcedony occurs in a wide range of varieties. Many semi-precious gemstones are in fact forms of chalcedony. The more notable varieties of chalcedony are as follows: agate (a variety of chalcedony with multi-colored curved or angular banding), aventurine (a form of quartz, characterized by its translucency and the presence of platy mineral inclusions that give a shimmering or glistening effect termed aventurescence), carnelian (a clear-to-translucent reddish-brown variety of chalcedony), chrysoprase (a green variety of chalcedony), heliotrope (a green variety of chalcedony, containing red inclusions), onyx (a variant of agate with black and white banding), but that list is not full.

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As early as the Bronze Age chalcedony was in use in the Mediterranean region; for example, on Minoan Crete at the Palace of Knossos, chalcedony seals have been recovered dating to circa 1800 BC. People living along the Central Asian trade routes used various forms of chalcedony, including carnelian, to carve intaglios, ring bezels (the upper faceted portion of a gem projecting from the ring setting), and beads that show strong Greco-Roman influence.

Chalcedony gemstones are valued for their strong color saturation and silky luster. Chalcedony is heat resistant and requires little care to maintain its translucent shine. It is rated a seven on the Mohs scale of mineral hardness, making it a durable option for daily-wear jewelry. Chalcedony jewelry is often made with silver and gold in rings, necklaces, earrings and bracelets. Chalcedony is also a complementary accompaniment to other gems in strands and clusters.