Called "the sailor's gem" and the "stone of courage," ancient Mediterranean sailors, fishermen, and sea travelers considered aquamarine to be a particularly lucky talisman for when on the water. Aquamarine amulets were believed to be especially powerful if the stone had an engraving of the moody Poseidon (Neptune to the Romans), god of the sea, and one of the symbols associated with him: dolphins, tridents or three-pronged fish spears.

Sea travelers carried aquamarine amulets to calm their fears in perilous situations and fishermen believed the amulets had the power to increase the size of their catch. And, in times of danger on the high seas, sailors believed the amulets would transfer unmatched bravery to their souls, giving them the power to overcome the most violent storm. The amulets were also thought to prevent seasickness, or at least lessen it.

Beryl, traditionally believed to be aquamarine, is one of the foundation stones of the New Jerusalem (New Testament) as well as one of the stones in the breastplate of Aaron, the High Priest (Old Testament): "...in the first row, a ruby, a topaz, and a beryl..." However, some Biblical scholars think every stone in the breastplate is conjecture as stone names and descriptions were haphazardly described until relatively recently. Rabbi Dr. Michael Samuel, in his article "Breastplate stones and tribal affiliation" speaks to the controversy surrounding beryl:

"Tarshish -- beryl, a precious stone of a sea-green color. Emerald and aquamarine are two types of beryl; it may also be citrine quartz or green jasper. The Septuagint calls this chrisolythos or berullion. In the Hellenistic period this name was applied to the topaz, a stone not known in the earlier periods. Now believed to have been identical with mother-of-pearl. Jerome's Vulgate translates it as the hyacinthus.

Beryl is a transparent gem of a bluish-green color, found in the East Indies [Saadia, Kimchi and the KJV]. Only the green beryl was known and used in Egypt in Moses' time, the aquamarine and the yellow and white beryls not being known. The name Tarshish is also the ancient Biblical name for Spain, and if this applies here, then we may assume that it is the yellow rock crystal or citrine quartz known as "chrysolith" according to Pliny (Natural History, xxxvii. 43)."

In the Middle Ages, aquamarine was believed to give the wearer both insight and foresight, as well as freedom from insomnia.

Water in which an aquamarine had been soaked was believed to cure eye troubles, stoppage of breath, and hiccups. It was also thought to reveal true friends versus false, by changing color.