Elbaite

Previous posts discussed the unique element concentrations and mineralization features of S-type granitic rocks formed during continental collision. Tourmaline, a well-known and visually striking gemstone, is commonly associated with hydrothermal veins in these peraluminous granitic systems.

The specimen shown here is elbaite, sourced from peraluminous granitic bodies intruded into the Beni Bousera peridotites and their surrounding amphibolite-to-granulite facies metamorphic envelope. U–Pb and ⁴⁰Ar/³⁹Ar dating reveal two major episodes of orogeny-related anatectic magmatism at approximately 300 Ma and 22 Ma. This locality presents an excellent case study of anatexis overprinting continental crustal segments that have already undergone high-grade metamorphism, partial melting, and melt extraction.

Although tourmaline from this particular locality has not been studied in detail, it holds significant potential for understanding the elbaite–schorl solid-solution series. In magmatic systems, schorl typically crystallizes early, while elbaite forms later through secondary crystallization. Elemental zoning in tourmaline crystals often shows increasing concentrations of Ca and Li from core to rim, while Mn²⁺ peaks in the intermediate zones before decreasing. These patterns suggest that tourmaline can serve as a sensitive recorder of trace element evolution and crystallization kinetics in granitic systems.

The specimen below features a well-developed pocket containing over a dozen multi-colored tourmaline crystals, each individually perched on a quartz and albite matrix.

Tourmaline on quartz and albite, 6.8 cm

Beni Bouzra, Chefchaouen Province, Tanger-Tetouan-Al Hoceima Region, Morocco

Jingnan (Tom) Zhang Coll & Photo