Paraíba Tourmaline - Geographic Origin Determination of Paraíba Tourmaline
- by Rajesh Kumar
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ABSTRACT
Vivid blue to green copper-bearing tourmalines, known as Paraíba tourmalines, are recovered from deposits in Brazil, Nigeria, and Mozambique. These tourmalines are sought after for their intense colors. Prices are based, in part, on the geographic origin of a stone, and determining provenance is thus an important aspect for Paraíba tourmaline. However, their geographic origin cannot be established by standard gemological testing and/or qualitative chemical analyses. GIA has established sophisticated criteria requiring quantitative chemical analyses to determine geographic origin for these tourmalines. These criteria were based on several hundred samples from known sources spanning the three countries. Highly accurate and precise quantitative elemental concentrations for Cu, Zn, Ga, Sr, Sn, and Pb are acquired with laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS). These data can then be plotted as a function of elemental concentration for accurate geographic origin determination.
INTRODUCTION
Copper-bearing gem tourmaline—recognizable by its vivid neon blue to green color—has been one of the most popular colored gemstones on the market for the nearly three decades since its debut (figures 1 and 2). It was first discovered in the state of Paraíba in northeastern Brazil in the late 1980s, and subsequently found in the neighboring state of Rio Grande do Norte (Fritsch et al., 1990; Shigley et al., 2001; Furuya, 2007). These gems became known as Paraíba tourmalines after the locality of their discovery. In the early twenty-first century, similarly colored gem-quality tourmalines were discovered in Nigeria and Mozambique (figures 3 and 4; Smith et al., 2001; Abduriyim and Kitawaki, 2005).
Read more... https://www.gia.edu/gems-gemology/winter-2019-paraiba-tourmaline-geographic-origin-determination
