Melanophlogite

specimen number:
2354152

location:
Mt. Hamilton, Santa Clara Co., California, USA

description:
Colorless gemmy crystals of melanophlogite to 0.2 cm in size on matrix. In good condition, choice thumbnail sized example for the species.

Located east of San Jose in the Diablo Range of Santa Clara County, California, the Mount Hamilton area features complex Franciscan Complex geology consisting of altered ultramafic rocks, serpentine, and silica-carbonate veins. Historical prospecting in the surrounding Black Wonder Mining District primarily targeted small manganese, quicksilver, and chromite deposits. Mineral collectors discovered an exceptionally rare occurrence of melanophlogite along Arroyo Bayo near Sugarloaf Mountain in the early 1970s. In this localized hydrothermally altered serpentine environment, low-temperature silica deposition trapped organic gases like methane and nitrogen inside a fragile silica clathrate framework. The site became famous among micromount collectors for producing sharp, lustrous, colorless to pale yellow cubic crystals of melanophlogite up to five millimeters across, resting on chalcedony, quartz, or cristobalite matrix. Because the locality lies on private ranchland and near protected watersheds, access for field collecting has historically been restricted, making preserved study specimens highly prized in mineralogical collections.

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