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Four colorless tourmalines of the liddicoatite-elbaite series from pegmatites from Anjanabonoina, Madagascar, have been characterized by crystal-structure determination and by chemical analyses. Optimized formulae range from  X (Ca 0.57 Na 0.29 □ 0.14 )  Y (Al 1.41 Li 1.33 Mn 2+  0.07 □ 0.19 )  Z Al 6  T (Si 5.86 B 0.14 )O 18  (BO 3 ) 3  V (OH) 3.00  W [F 0.76 (OH) 0.24 ] [a = 15.8322(3), c = 7.1034(3) Å] to  X (Na 0.46 Ca 0.30 □ 0.24 )  Y (Al 1.82 Li 0.89 Fe 2+  0.01  Mn 2+  0.01 □ 0.27 )  Z Al 6  T (Si 5.56 B 0.44 )O 18  (BO 3 ) 3  V (OH) 3.00  W [(OH) 0.50 F 0.50 ] [a = 15.8095(9), c = 7.0941(8) Å] (R = 1.3.1.7%). There is a high negative correlation (r 2  = 0.984) between the &lt;T-O&gt; bond-lengths (~1.618.1.614 Å) and the amount of  IV B (from the optimized formulae). Similar to the olenites (from Koralpe, Austria) the liddicoatite-elbaite samples show a positive correlation between the Al occupancy at the Y site and  IV B (r 2  = 0.988). Short-range order configurations show that the presence of  IV B is coupled with the occupancy of (Al 2 Li) and (Al 2 □) at the Y site. The structural formulae of the Al-rich tourmalines from Anjanabonoina, Madagascar, show ~ ⃞ 0.2  (vacancies) on the Y site. We believe that short-range order configurations with Y(Al 2 □) are responsible for these vacancies. Hence, an oft-used calculation of the Li content by difference on the Y site may be problematic for Al-rich tourmalines (olenite, elbaite, rossmanite). Fourier transform infrared (FTIR) spectra were recorded from the most  IV B-rich tourmaline sample. The bands around 5195 and 5380 cm -1  can be assigned to H 2 O. Because these bands still could be observed in FTIR spectra at temperatures from -150 to +600 °C, it seems unlikely that they result from H 2 O in fluid inclusions. Interestingly, another FTIR spectrum from a dravite in which the X site is filled completely with Na, does not show bands at ~5200 and ~5400 cm -1 . Although not definitive, the resulting spectra are consistent with small amounts of H2O at the X site of the elbaite. The rare-earth element (REE) pattern of the B-rich elbaite (ΣREE: ~150 ppm) demonstrates that this sample is strongly enriched in LREEs compared to HREEs and exhibits a negative Eu anomaly. This sample shows the strongest enrichment of LREEs and a high La N /Yb N  ratio of ~351, which seems to confirm an important role of the fractional crystallization process.

american mineralogist

Tetrahedrally coordinated boron in tourmalines from the liddicoatite-elbaite series from Madagascar: Structure, chemistry, and infrared spectroscopic studies