Amphiboles along the tremolite-pargasite join have been hydrothermally synthesized at 900°C, 3 kbar. Run products were characterized by optical and electron microscopy, powder X-ray diffraction and infrared spectroscopy. Under the experimental conditions used, there is complete solid-solution between tremolite and pargasite and the variation of cell parameters is linear as a function of composition. The infrared spectra in the principal OH-stretching region are consistent with the predictions of Hawthorne (1997) on local bond-valence grounds, and show strong short-range order of cations at the octahedral sites and strong coupling between Al at T(l) and Na at A.

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