Lepidolite after Elbaite

specimen number:
9862036

location:
Minas Gerais, Brazil

description:
Prismatic crystal of what was once elbaite almost 6.0 cm in length now replaced by crystallized lepidolite. This is set on a quartz matrix.

Minas Gerais, Brazil, is globally renowned as one of the most important pegmatite provinces in the world, stretching primarily across the eastern and northeastern portions of the state. Geologically, these complex granitic pegmatites formed during the Neoproterozoic to early Paleozoic eras as a result of the regional Araçuai Orogeny, where intense metamorphic and tectonic activity forced volatile- and rare-element-rich melts into surrounding schist and gneiss formations. These conditions created wide zones containing giant crystal pockets rich in lithium, beryllium, tantalum, and gemstones. Historically, mining in the region began with colonial gold and diamond prospecting in the 17th and 18th centuries, but expanded dramatically into systematic pegmatite extraction during the 19th and 20th centuries, fueled by global demand for industrial minerals and exceptional gem specimens that continue to supply collectors and museums worldwide.

Pseudomorphs of lepidolite after elbaite occur when hydrothermal fluids or late-stage pegmatitic fluids alter pre-existing tourmaline crystals, replacing the original boro-silicate structure with pink, lilac, or silvery lithium-bearing mica. Geologically, this transformation typically takes place in evolved granitic pegmatites during the final phases of crystallization, where changing chemical conditions, such as an increase in potassium and lithium alongside falling temperatures, destabilize the tourmaline. Mineralogically, the resulting specimens preserve the external prismatic, striated crystal form of the original elbaite while completely substituting the interior with scaly, fine-grained aggregates of lepidolite, creating highly prized collector pieces that record the dynamic fluid evolution of pegmatite systems.

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