ABOUT THE SPECIMEN
Masses of zincite crystals interspersed along a mix of franklinite and willemite. There's also a little bit of the rare mineral sussexite present on the back. With shortwave UV, the willemite pops with that neon green glow that the species is famous for. The Franklin mines are the type locality for zincite, franklinite, and sussexite, and the first two are the most recognizable species from the mines. Classic combination piece from one of the most recognizable locales in the world.
VIDEO
MORE INFO
Hot metalliferous brines discharged onto a shallow Proterozoic seafloor roughly 1.3 billion years ago deposited the metal-rich sediments that would eventually become the Franklin ore body - subsequent burial to 15–18 km during Grenvillian orogenesis drove temperatures to 750–800°C, recrystallizing the original carbonates into Franklin Marble and transforming those metal-rich layers into franklinite, willemite, and zincite. Franklinite is a zinc-iron-manganese oxide of the spinel group whose jet-black metallic octahedral crystals are largely opaque and non-fluorescent - the iron and manganese suppress luminescence - but occur in dramatic contrast against the deep red of zincite, which derives its color from manganese substitution in the zinc oxide structure. Genuinely large euhedral franklinite crystals are uncommon; the mineral more typically occurs as disseminated granular masses in calcite groundmass, while zincite forms compact hexagonal prisms or anhedral masses associated with it. The Franklin Mine closed in 1954, with Sterling Hill following in 1986, and 359 confirmed species have been documented across the two operations - 19 found nowhere else on earth. Combination specimens with both franklinite and orange zincite on white calcite matrix represent one of the most distinctly American collector pieces in existence.