Structural defects in synthetic tremolitic amphiboles

Synthetic hydroxyl tremolite, fluor-tremolite, and magnesio-hornblende together with two natural tremolite samples were investigated using high-resolution transmission electron microscopy (HRTEM). Chain-width defects are widespread in both hydroxyl tremolite and magnesio-hornblende synthesized at pressures and temperatures ranging from 2 to 10 kbar and 701 to 853°C. In contrast, fluorine tremolite synthesized at 2.13 kbar and 1000°C is virtually free of such defects, similar to natural tremolite that is completely ordered. The degree of structural ordering is given for each mineral. Temperature is apparently the most critical experimental variable affecting the number of chain-width defects in synthetic amphiboles. In addition, the seeding technique using defect-free natural tremolite greatly increases the structural order in synthetic amphibole. -from Authors