Stilbite is a tectosilicate mineral of the zeolite group, and is a series name rather than a specific mineral. There is a series between Stilbite-Ca and Stilbite-Na. Stilbite-Ca is NaCa4(Si27AL9)O72 . 28(H2O), and Stilbite-Na is Na9(Si27Al9)O72 . 28(H2O) Zeolites have a porous structure which can accomodate a wide range of cations, i.e. Na+, Ca2+, K+, etc.,Which explains why the zeolites are so complex, and not always easy to identify outside the laboratory. This specimen was brought back from the Isle of Skye by one of our members.