Cyclosilikaadid

Cyclosilikaadid, or cyclosilicates, are a class of silicate minerals in which the silicon-oxygen tetrahedra link together to form cyclic units, typically six-membered rings (Si6O18). These rings carry a negative charge that is balanced by various metal cations such as aluminum, magnesium, iron, lithium, beryllium, and other alkali or alkaline-earth elements. The resulting minerals exhibit a range of compositions but share the characteristic cyclic silicate structure.

The fundamental structural feature of cyclosilicates is the presence of discrete ring units built from SiO4 tetrahedra. Depending on composition, these rings may arrange to form three-dimensional frameworks or layered structures, but the ring is the defining motif. The rings are often accompanied by boron, aluminum, or other cations that occupy specific sites in the crystal lattice, influencing color, hardness, and stability.

Notable minerals in this group include beryl, with the formula Be3Al2Si6O18, which yields gemstones such as emerald and aquamarine. The tourmaline group also falls within the cyclosilicate category and is known for its complex composition and pleochroism. Other cyclosilicates encompass a broader range of compositions and crystal systems, but all share the common ring-based silicate framework.

Cyclosilicates occur in a variety of geological environments, including igneous and metamorphic rocks, pegmatites, and hydrothermal deposits. They are valued in gemology (beryl varieties) and studied for their distinctive crystallography and the influence of trace elements on color, transparency, and physical properties.