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
USS Aquamarine (PYc-7) named for the gemstone aquamarine. Assigned to the Naval Research Laboratory, Bellevue, D.C., "Aquamarine" assisted in experimental work, chiefly underwater sound. Although most of her experiments were conducted on the Potomac River and Chesapeake Bay, she also operated off New London, Connecticut, from 16 October to 4 November 1943, and off the Florida coast and in the Bahamas from 24 January 1944 to 18 April 1945. During 1945 and 1946 "Aquamarine" had additional duty as special tender to the presidential yachts and . "Aquamarine" was decommissioned on 21 June 1946 and transferred to the Maritime Commission on 31 January 1947