Cyclosilicate structure, illustration. The cyclosilicate anion, Si6O18(-12), is a 12-membered crown-shaped ring of six tetrahedral silicon atoms (lavender) alternating with six bridging oxygen atoms (red). Each silicon atom is also bonded to two outer oxygen atoms. Cyclosilicate is found combined with a variety of metal cations in several minerals, with beryl (Be3Al2Si6O12) being the most familiar example.