Aquamarine beads Color: blue Sizes between 4 and 12 mm. Country of origin: Madagascar. Treatment: contains colourless oil and resin residues that are present in small stone fractures. Aquamarine gemological information: Possible colors: light blue to dark blue, blue-green. Density: between 2.68 and 2.80. Hardness: 7.5 Crystal system: hexagonal. Break: conchoidal. Cleavage: imperfect. Polariscope: anisotropic (restores all 90°, except in the optical axis). Refractive index: No: 1,572 to 1,590. Ne: 1.567 to 1.583. Beryl Maxixe: 1.584 to 1.593 Birefringence: 0.006 to 0.0009. Beryl max.: 0.008. Chelsea filter: more intense green or blue. Spectrum: some of the aquamarines shown may have bands around 427 nm, 456 nm, sometimes 537 nm. These bands are absent in case of heating. Existing treatments to modify aquamarine: heating, radiocobalt irradiation.