Aquamarine is a blue or cyan variety of beryl. It occurs at most localities which yield ordinary beryl. The gem-gravel placer deposits of Sri Lanka contain aquamarine. Chrysolite aquamarine is a green-yellow stone, occurring in Brazil. Maxixe is a deep blue version of aquamarine, commonly found in the country of Madagascar. Its color fades to white under sunlight. It can also fade because of heat treatment. The color can returns with irradiation tratement.
The pale blue color of aquamarine is attributed to Fe2+. Fe3+ ions produce golden-yellow color, and when both Fe2+ and Fe3+ are present. The color is a darker blue as in maxixe. Decoloration of maxixe by light or heat thus may be due to the charge transfer between Fe3+ and Fe2+. Dark-blue maxixe color can be produced in green, also pink or yellow beryl by irradiating it with high-energy particles. Gamma rays, also neutrons or even X-rays.
The chemical composition of Beryl is beryllium aluminium cyclosilicate with the chemical formula Be3Al2(SiO3)6. Well-known varieties of beryl include emerald, also aquamarine, heliodor, and morganite. Naturally occurring, hexagonal crystals of beryl can be up to several meters in size. Terminated crystals are relatively rare. Pure stone is colorless, the color is due to inclusions. Possible colors are green, blue, yellow, red (the rarest), and white. It is also an ore source of beryllium.
Beryl belongs to the hexagonal crystal system. Normally it forms hexagonal columns but can also occur in massive habits. As a cyclosilicate it incorporates rings of silicate tetrahedra that are arranged in columns along the C axis and as parallel layers perpendicular to the C axis, forming channels along the C axis. These channels incorporate a variety of ions, neutral atoms, and molecules into the crystal. Thus disrupting the overall charge of the crystal permitting further substitutions in Aluminium, Silicon, and Beryllium sites in the crystal structure. The variety of colors comes from impurities. Increasing alkali content within the silicate ring channels causes increases to the refractive indices and birefringence.