Mineral site, and from there further subdivided by the chemistry of the W site. The Y and Z sites can accommodate a variety of cations, especially various transition metals; this variability in structural transition metal content gives the tourmaline group greater variability in colour. Other cyclosilicates include beryl, AlBeSiO, whose varieties include the gemstones emerald (green) and aquamarine (bluish). Cordierite is structurally similar to beryl, and is a common metamorphic mineral. Sorosilicates, also termed disilicates, have tetrahedron-tetrahedron bonding at one oxygen, which results in a 2:7 ratio of silicon to oxygen. The resultant common structural element is the [SiO] group. The
Dom Pedro aquamarine of Natural History's Janet Annenberg Hooker Hall of Geology. Dom Pedro aquamarine The Dom Pedro aquamarine is the world's largest cut aquamarine gem. It was cut from a crystal originally weighing approximately and measuring more than in length. The stone was mined in Pedra Azul, in the state of Minas Gerais in Brazil around 1980, and named after the Brazilian emperors Pedro I and Pedro II. The blue-green gemstone was cut by Bernd Munsteiner into an obelisk form weighing 10,363 carats. The finished dimensions measure tall by wide. The jewel was donated to the Smithsonian Institution by Jane Mitchell and