Pegmatitos graníticos são fonte de numerosos minerais com elevado potencial gerador de variedades de boa qualidade gemológica, com destaque para berilo, várias espécies do super-grupo da turmalina, topázio, espodumênio, quartzo, feldspatos, além de outros minerais menos comuns {p. ex. granadas, euclásio, gahnita, tantalita-(Mn), microlitas}. Na Província Pegmatítica da Borborema (PPB), alvo deste estudo, destacam-se as turmalinas, incluindo a famosa "turmalina Paraíba, berilo, quartzo, espessartita, gahnita, euclásio, como minerais de bom potencial gemológico. A formação destas gemas na PPB, assim como na maioria das Províncias Pegmatíticas mundiais, é localizada em cavidades situadas preferencialmente na transição entre a zona intermediaria interna e o núcleo de quartzo de pegmatitos heterogêneos mais diferenciados. A descrição das principais ocorrências de gemas da PPB será objeto deste trabalho.

A first occurrence of a nigerite-group mineral in the Borborema Pegmatite Province, at the Roncadeira pegmatite, Nova Palmeira county, State of Paraíba is described. It is the second one in Brazil after the first finding in the State of Amapá, in the regolith covering pegmatites close to the Jornal Village at the Parapuerí river, south of the Serra do Navio Mn-deposit. The specimens of the Amapá occurrences had been identified "sensu lato" as nigerite by wet chemical analyses without specification according to the nomenclature approved much later by the IMA (International Mineral Association) for the nigerite-högbomite supergroup. The Roncadeira occurrence was already mentioned earlier by the authors without details and identification embased on the chemical composition obtained by semi-quantitative SEM (scanning electron microscopy) followed by electron microprobe analyses (EMPA) and RAMAN spectra. The stoychiometric formula obtained by the average of thirteen EMPA data (on three grains), normatized for a total of 11 cations is Sn0.95Ta0.04 (Zn1.14, Fe0.69, Mg0.09, Mn0.10 , Ca 0.02)2.04 Al7.85Si0.11O15 (OH) The average of the cationic ratios Zn/(Zn+Fe+Mn+Mg+Ca) = 0.56, and Zn/Fe = 1.65 are not compatible with ferro-or magnesionigerite and Al/Sn =8.27 (higher than 7.0) is typical for the 6N6S polysome, inadequate for the 2N1S polysome. These values would therefore allow to classify the nigerite group mineral from Roncadeira as "zinconigerite-6N6S" still not recognized as a valid species by IMA, but with similar chemistry found in other eight occurrences worldwide. The "zinconigerite" from Roncadeira occurs in paragenetic association with cassiterite, tapiolite-(Fe), ferrowodginite, ferrotitanowodginite and gahnite in both, the greisen-like border zone and in albite-rich replacement bodies in the inner pegmatite zones. In sheared portions this paragenesis is associated also with crysoberyl and sillimanite, features very similar to those registered at the type-locality in Nigeria and in Namibia, Portugal, Brazil (Amapá), Canada, Finland (Rosendal). All these occurrences are therefore possibly related with late contact-metamorphic-metassomatic processes of the host pegmatites.