Quartz (repaired)

specimen number:
2292412

location:
PC Mine, Basin, Montana, USA

description:

A glassy gem colorless Japan law twin crystal 4.0 cm across on a breccia matrix with many non-twinned quartz crystals. The piece has been repaired.

The PC Mine, located near Basin in Jefferson County, Montana, is a historic underground mine that operated primarily during the late nineteenth and early twentieth centuries. Geologically, it is situated within the Boulder Batholith, a massive Cretaceous-aged granitic intrusion that hosts extensive networks of polymetallic quartz veins. These mineralized veins were deposited by hydrothermal fluids flowing through tectonic fracture systems, concentrating economic deposits of lead, zinc, silver, and gold. Historically, the PC Mine contributed to the region's rich mining output, and like many neighboring sites in the Basin mining district, its legacy involves both its past metal production and subsequent environmental remediation efforts to manage acidic mine drainage.

A Japan law twin is a rare, highly symmetrical growth form of quartz where two individual crystals share a specific crystallographic contact plane. Under this particular twin law, the two crystals meet at a precise angle of 84 degrees and 33 minutes, typically forming a flat, V-shaped or butterfly-like structure. This contact twinning occurs at the earliest nucleation stages of crystal growth, often triggered by rapid crystallization under high-supersaturation conditions in hydrothermal veins. Due to their distinct geometric shape and extreme rarity compared to standard intergrown quartz clusters, Japan law twins are highly sought after by mineral collectors.

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