The magnetic properties of silicates and phosphates are compiled in subvolume 27I. While subvolumes 27I1, 27I2, 27I3, 27I4, and 27I5 (already published) deal with orthosilicates, sorosilicates, cyclosilicates, inosilicates, and phyllosilicates, respectively, the present subvolume 27I6 deals with tectosilicates. Subvolume 27I6 has been split in three parts α,ß  and  γ. Further subvolumes will be dedicated to phosphates. – Silicates are very complex systems, covering large classes of minerals as well as synthetic samples. Their crystal structure is discussed and atomic positions are given. In addition to magnetic properties, results of neutron diffraction studies, nuclear gamma resonance, nuclear magnetic resonance, X-ray absorption spectroscopy, transport properties, dielectric and optical data are reviewed.