cyklosilikaadid

Cyclosilicates are a subclass of silicate minerals characterized by the presence of a ring-shaped structure of linked SiO4 tetrahedra. In these structures, each tetrahedron shares two corner oxygen atoms with adjacent tetrahedra, forming closed rings. The size of these rings can vary, with common examples being rings of three, four, or six tetrahedra. The general formula for cyclosilicates is based on the number of tetrahedra in the ring. For a ring of n tetrahedra, the formula is typically M_x^n(Si_nO_{3n}) where M represents cations.

The simplest and most common cyclosilicates are the benitoite group, which feature six-membered rings (Si6O18). Another important group is the tourmaline group, which also contains six-membered rings but with a more complex composition and charge balance. Micas, while often considered phyllosilicates due to their layered structures, contain [Si4O10] sheets that can be conceptually broken down into smaller cyclic units. The linkage of these tetrahedral rings within the crystal structure dictates the overall properties and cleavage of cyclosilicate minerals.

Cyclosilicates are found in a variety of geological environments. For example, beryl, known for its gem varieties like emerald and aquamarine, is a cyclosilicate with hexagonal rings and is often found in granitic pegmatites. Cordierite, another cyclosilicate, is an important rock-forming mineral in metamorphic rocks. The presence and type of cations that balance the negative charge of the silicate rings significantly influence the physical properties such as hardness, density, and color of these minerals.