Ramanite-(Cs) and ramanite-(Rb): New cesium and rubidium pentaborate tetrahydrate minerals identified with Raman spectroscopy

Abstract

This study of melt and fluid inclusions in graphic pegmatite quartz from the Island of Elba, Italy has identified silicate melts and coexisting aqueous fluid from the final stage of pegmatite formation, which contain extremely high concentrations of boron (up to 19.8 mass% B 2 O 3 ), cesium (>5 mass% Cs 2 O), and rubidium (>0.5 mass% Rb 2 O). Several boron-bearing minerals have been identified in melt and fluid inclusions, including sassolite (H 3 BO 3 ) and santite (KB 5 O 8 ·4H 2 O). In addition, we have found two new minerals observed as daughter mineral phases, and these have been accepted by the IMA, Commission on New Minerals, Nomenclature and Classification (CNMNC) as ramanite-(Cs) (2007-007), monoclinic β-cesium pentaborate tetrahydrate (CsB 5 O 8 ·4H 2 O) with space group C2/c, and ramanite-(Rb) (2007-006), orthorhombic rubidium pentaborate tetrahydrate (RbB 5 O 8 ·4H 2 O) with space group Aba2.At the moment, given sample constraints, we cannot directly determine some of the properties traditionally reported for new minerals; however, both phases have Raman spectra identical to spectra obtained on synthetic Cs and Rb pentaborates, which were studied for comparison. Although difficult to recognize optically, ramanite-(Cs) and ramanite-(Rb) have distinctive Raman spectra allowing simple and definitive identification from other translucent phases found in many hypersaline fluid inclusions. Although currently only identified from a limited number of occurrences, given the availability of a definitive means of identification, we suspect that ramanite-(Rb) and ramanite-(Cs) may in fact be common, at least in boron-rich pegmatites.

Structural and spectroscopic properties of new noncentrosymmetric self-activated borate Rb3EuB6O12 with B5O10 units

“…An asymmetric stretching of BO4 should be observed in Raman spectra in the range of 1000-1150 cm -1 , however, intensity of these bands are very weak [50], in the case of Infrared spectra these vibrations are clearly observed at 975-1100 cm -1 . Raman bands in the region of 725-800 cm -1 are symmetric stretching of BO4 and strong line at 756 cm -1 can be used as an indicator of the pentaborate group presence [52]. Symmetric stretching of BO4 in the range of 750-810 cm -1 can be found in Infrared spectra.…”

Water- and Boron-Rich Melt Inclusions in Quartz from the Malkhan Pegmatite, Transbaikalia, Russia

“…As well as the generally high boric acid concentration there are often very Cs-rich inclusions, with Cs in the form of the Cs pentaborate mineral, ramanite-(Cs)-see Thomas et al [28]. By calculations according to Gmelin [29] the melting temperature, t S = 101.8 ± 5.3 °C of 12 inclusions gives a Cs pentaborate concentration of 23.8% (g/g) (see Figure 7) or a Cs concentration of 10.04% (g/g), a 20,000 fold enrichment against the mean content of granitic rocks.…”

“…By calculations according to Gmelin [29] the melting temperature, t S = 101.8 ± 5.3 °C of 12 inclusions gives a Cs pentaborate concentration of 23.8% (g/g) (see Figure 7) or a Cs concentration of 10.04% (g/g), a 20,000 fold enrichment against the mean content of granitic rocks. Data in the Figure 7b for the Elba pegmatite [28] and Rangkul pegmatite [30] are given for comparison. The second point for the Malkhan pegmatite represents late-stage fluid inclusions for comparision.…”

Nyerereite and nahcolite inclusions in diamond: evidence for lower-mantle carbonatitic magmas

“…Some inclusions were identified with the aid of Raman spectroscopy, which is a non-destructive, high-sensitivity technique requiring minimal sample volume and preparation (e.g. Thomas et al, 2008). Raman spectra were recorded at the GFZ Potsdam with a Jobin-Yvon LabRam HR800 spectrometer (grating: 1200 gr mm À1 ), equipped with an Olympus optical microscope and a longworking-distance LMPlanFI 1006/0.80 objective.…”