Strontiojoaquinite

specimen number:
2282078

location:
Numero Uno Mine, San Benito Co., California, USA

description:
Tiny yellowish micro crystals of strontiojoaquinite on matrix. Collected by Chuck Trantham in 2015.

The Numero Uno mine, located along the south side of Clear Creek near San Benito Mountain in San Benito County, California, is a historic prospecting locality famed for its highly unusual barium-strontium-titanium silicate mineralogy. Geologically, the deposit consists of a tabular blueschist body or lens enclosed within a massive, regionally metamorphosed serpentinite matrix belonging to the New Idria district. Mineralization occurred when high-pressure, low-temperature hydrothermal fluids altered the blueschist fractured zones, depositing specialized silicates and crosscutting veins within the host rock. Though initially staked during the early twentieth century following the nearby 1907 discovery of benitoite, the site was worked primarily through sporadic, small-scale exploratory tunneling and trenching by independent prospectors rather than large-scale industrial corporate mining, with active field development peaking intermittently in the mid-to-late twentieth century.

Strontiojoaquinite is a rare secondary barium strontium sodium iron titanium silicate mineral that typically develops within these highly specialized, alkaline hydrothermal veins cutting through altered blueschist. Geologically, it forms as late-stage crystals under precise metamorphic conditions, often developing directly as overgrowths on top of existing joaquinite-Ce cores or in close association with minerals like neptunite, natrolite, and albite. The mineral typically manifests as transparent to semitransparent microcrystals with a distinct vitreous luster, commonly exhibiting pseudotetragonal, steeply dipyramidal forms that range in coloration from a light yellowish-green to a rich yellow-brown.

Charles "Chuck" Trantham (1937-2020) was a prominent California geologist, field collector, and mineral dealer who assembled a significant private collection over several decades of active field exploration. Known for his methodical field-collecting excursions across the western United States, he frequently self-collected exceptional specimens from notable California localities and maintained a highly respected presence within regional mineral societies and national exhibitions.

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