DISTINCT DOMAINS IN "GUARINITE" FROM MONTE SOMMA, ITALY: MICROSTRUCTURAL HRTEM EVIDENCE

“Guarinite” crystals, of composition Na 1.56 Ca 11.13 Zr 2.33 Nb 0.07 Mn 0.51 Fe 0.40 (Si 2 O 7 ) 4 (O 3.31 F 4.69 ), 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., null Si 2 O 7 null groups), possibly shifted by null c /2 within the framework of...