Aquamarine (from the Latin phrase "aqua marina" which means "sea water"; has been named after the colour * EN: aquamarine; DE: Aquamarin; FR: aigue-marine; ES: aguamarina; RU: аквамарин) is the mineral, slightly alkaline variety of beryl of greenish, pale or intense light blue colour. The coloration is caused by the admixture of the Fe2+ ions, which are replacing aluminium in the octahedral sites, and are interacting with the transfer of the charge by the Fe3+ ions, which are located mainly in the structural channels of the mineral.

It is characterised by the pleochroism, which is taken into account during the cut. The jewellery grade sky-blue aquamarines are mainly produced by the annealing or irradiation of the transparent crystals of the more abundant yellow-green beryl. The habit of the crystals of aquamarine is columnar, long-prismatic.

The crystal of aquamarine of the largest size (110.5 kilograms) has been found in Brazil (Minas Gerais state).

Aquamarine is found in the miarolitic granitic pegmatites (Brazil, Madagascar; in the USSR in Ukraine), less often in the mica-quartz greisens (Sherlovaya mountain in the Trans-Baikal region). Aquamarine is the gemstone of the III order.