Tremolite synthesis from CaCl2-bearing aqueous solutions
Zimmermann, Rolf; Heinrich, Wilhelm; Rranz, Gerhard
European Journal of Mineralogy Volume 8 Number 4 (1996), p. 767 - 776
published: Jul 29, 1996
manuscript accepted: Feb 29, 1996
manuscript received: Sep 8, 1995
ArtNo. ESP147050804010, Price: 29.00 €
Abstract Tremolite of the average composition tremolite95 - Mg-cummingtonite5 and a compositional range between tremoliteioo and treço - Mg-cumio has been synthesized from oxide/hydroxide mixtures in the presence of CaCl2-bearing solutions. The crystals are up to 900 x 40 x 15 μm in size, and typically between 50 and 300 μm long, thus easily permitting accurate electron microprobe analysis. They are free of chain multiplicity faults. Lattice parameters are a = 9.824 (1) Å; b = 18.061 (2) Å; c = 5.279 (1) Å; ß = 104.627 (5)°; V = 906.36 (1) Å3. Together with tremolite, traces of diopside + quartz or diopside + talc + quartz also crystallized. The formation of the tremolite-Mg-cummingtonite solid solutions results from divariant breakdown of tremolite to tremolite-Mgcummingtonitess + diopside + quartz, the latter representing the stable assemblage at 800°C/2kbar. The synthetic tremolites clearly vary along the MgCa-1 exchange vector. Their compositional range is explained by fractional crystallization in the fluid caused by temporal and spatial variations of the effective bulk composition in the course of a dissolution - precipitation process.