Abstract
"Guarinite" crystals, of composition Na1.56Ca11.13Zr2.33Nb0.07Mn0.51Fe0.40(Si2O7)(4)(O3.31F4.69), show extensive defective microstructural arrangements, deriving from the presence of domains with different unit-cells. The structural complexity of "guarinite" results from the variable arrangements of simple structural building units (i.e., Si2O7 groups), possibly shifted by c/2 within the framework of octahedra. Actually, [100] and [010] images acquired with a transmission electron microscope reveal ubiquitous lamellar microstructures. Interlocked irregular domains characterize the [001] projection.