Abstract A series of aluminous tremolites was synthesized at 800-850 °C and 6-13 kbar along the join Ca1.8Mg5.2Si8O22(OH)2-Ca1.8(Mg4.2Al)(AlSi7)O22(OH)2 by means of the Mg-Tschermaks substitution. Although the amphibole yields were high (97-99 wt%), traces of orthopyroxene, clinopyroxene, amorphous silica, and, for the most aluminous mixture, corundum, were identified in some synthesis products. The samples were characterized by electron microprobe (EMP), X-ray diffraction Rietveld structure refinement (XRD), Fourier- transform infrared (FTIR) spectroscopy, and magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy for the purpose of identifying the extent of Al, Mg, and Si order-disorder in the octahedral and tetrahedral sites. Both EMP and 27Al NMR verify that the Mg-Tschermaks substitution, with even distribution of Al between tetrahedral and octahedral sites, is obeyed in these amphiboles up to a limit of 1.9 total Al atoms per formula unit (apfu). 29Si MAS NMR spectra indicate that Al substitutes essentially equally into both the T1 and T2 sites. For octahedral sites, the FTIR spectra indicate the presence of Al on the M1, M3, or both sites (presently indistinguishable) by the presence of an (MgMgAl)-OH band at 3652 cm-1, which increases steadily with increasing Al content. The FTIR and 27Al MAS NMR spectra show that Al is always present in the M1-M3 sites as well as the M2 site but partitioned among these sites in ways that are not clearly resolved at present. It is clear in this study that Al is more widely distributed over the octahedral and tetrahedral sites in synthetic aluminous tremolite with only a moderate Al content (< 2.0 Al apfu) than has been traditionally thought.

Tsaregorodtsevite [N(CH3)4][Si2(Si0.5Al0.5)O6]2 is a unique feldspathoid with a tetramethylammonium (TMA1) organic cation in an ordered, sodalite-like framework of orthorhombic symmetry (I222) with a 5 8.984(3), b 5 8.937(2), and c 5 8.927(2) Å. Here, 13C cross polarization MAS and 1H MAS NMR spectra give direct evidence that the organic material in the cavities in tsaregorodtsevite is TMA1. The 27Al and 29Si MAS NMR spectra, and XRD data show that the framework is well ordered with Si in the T1 and T2 sites and both Si and Al in the T3 site. Upon heating, the colorless tsaregorodtsevite crystals change color becoming yellow, then brown, and finally black. In this study 1H, 13C, 27Al, and 29Si MAS NMR, powder XRD, and electron microprobe analyses are used to investigate the structural changes in tsaregorodtsevite on heating. The cell dimensions and T-O bond lengths decrease, and there are two phase changes. At 690 8C, the TMA1 molecule breaks down to form aromatic rings and acidic groups, possibly including benzene and the pyridinium ion, with ammonia and other gases produced. The Al-Si framework changes slightly to give a less well-ordered tetragonal structure (I422), with a 5 8.925(1), c 5 8.908(1) Å, and a small amount of Al enters a separate phase. After heating at 970 8C, the organic material has further broken down with little C and H visible by NMR spectroscopy. The Al-Si framework forms at least two new phases: one with a cubic crystalline structure (I432) with a 5 8.817(3) Å, and an amorphous aluminosilicate phase. There is a small residue of the initial structure even after heating for one hour at over 900 8C.

Tsaregorodtsevite [N(CH3)(4)][Si-2(Si0.5Al0.5)0(6)](2) is a unique feldspathoid with a tetramethylammonium (TMA(+)) organic cation in an ordered, sodalite-like framework of orthorhombic symmetry (I222) with a=8.984(3), b=8.937(2), and c=8.927(2) Angstrom. Here, C-13 cross polarization MAS and H-1 MAS NMR spectra give direct evidence that the organic material in the cavities in tsaregorodtsevite is TMA(+). The Al-27 and Si-29 MAS NMR spectra, and XRD data show that the framework is well ordered with Si in the T1 and T2 sites and both Si and Al in the T3 site. Upon heating, the colorless tsaregorodtsevite crystals change color becoming yellow, then brown, and finally black. In this study H-1, C-13, Al-27. and Si-29 MAS NMR, powder XRD, and electron microprobe analyses are used to investigate the structural changes in tsaregorodtsevite on heating. The eel dimensions and T-O bond lengths decrease, and there are two phase changes. At 690 degrees C, the TMA(+) molecule breaks down to form aromatic rings and acidic groups, possibly including benzene and the pyridinium ion, with ammonia and other gases produced. The Al-Si framework changes slightly to give a less well-ordered tetragonal structure (1422), with a=8.925(1), c=8.908(1) Angstrom, and a small amount of Al enters a separate phase. After heating at 970 degrees C, the organic material has further broken down with little C and H visible by NMR spectroscopy. The Al-Si framework forms at least two new phases: one with a cubic crystalline structure (I432) with a=8.817(3) Angstrom, and an amorphous aluminosilicate phase. There isa small residue of the initial structure even after heating for one hour at over 900 degrees C.