Abstract
Quartz from La Sassa (Tuscany, Italy) presents a unique luminescence related to intrinsic and extrinsic defects in the crystal lattice due to the growth mechanisms in hydrothermal conditions. The bright fluorescence under the UV lamp was apparent to collectors since the early 1970s, and it entered the literature as a reference case of yellow-luminescent quartz. Early reports present the history of the discovery, the geological context, and preliminary luminescence measurements of the quartz nodules, suggesting various activators as potentially responsible of the peculiar luminescence effects: uranyl groups (UO22+), rare earths (Tb3+, Eu3+, Dy3+, Sm3+, Ce3+) and polycyclic aromatic compounds (PAH). Here, we report a full investigation of the La Sassa material, by a multi-analytical approach encompassing cathodoluminescence optical microscopy (OM-CL), laser-induced fluorescence (LIF), wavelength resolved thermally stimulated luminescence (WR-TSL), trace elements analysis by mass spectrometry (ICP-MS) and Raman spectroscopy (RS). The results provide a significant step forward in the interpretation of the luminescence mechanisms: the main luminescent centres are identified as alkali-compensated (mainly Li+ and Na+, K+ and H+) aluminum [AlO4/M+]0 centres substituting for Si, where the recombination of a self-trapped exciton (STE) or an electron at a nonbridging oxygen hole centre (NBOHC) are active.
Highlights
In the early 1970s, a small deposit of bright luminescent quartz was discovered in a calcite/dolomite outcrop near the town of La Sassa, Tuscany (Italy)
Cathodoluminescence images of the La Sassa sample (Figure 3) show bright luminescence colours related to distinct phases of crystal growth
The blue-purple luminescence seems to follow the concentric growth layers being limited by the single rims, whereas the luminescence centres responsible for the bright light green colour are scattered over the section crossing layers in different directions
Summary
In the early 1970s, a small deposit of bright luminescent quartz was discovered in a calcite/dolomite outcrop near the town of La Sassa, Tuscany (Italy). It has been defined as a “unique form of fluorescing quartz” showing “a unique response under UV light, in terms of intensity and quality of the excitation spectra” [1]. Luminescence investigations are widely applied to the study of hydrothermal mineralization processes, and the data are often interpreted in relation to fluid inclusion microthermometry, trace element incorporation, and isotopic variability [6,8,9,10,11]. On the basis of these early measurements, Dallegno and Mazzoleni [1,15]
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