Quartz

specimen number:
2292138

location:
Denny Mt., King Co., Washington, USA

description:
Colorless crystals of scepter quartz to 4.5 cm in height coming off matrix. The crystal terminations are slightly amethystine. In good condition. Collected in 1986.

The Denny Mountain locality, situated near Snoqualmie Pass in King County, Washington, is a classic alpine mineral occurrence renowned for its large amethyst and quartz crystals. Geologically, the mountain features an extensive contact metamorphic skarn zone produced where the Miocene-aged Snoqualmie Batholith intruded into older Paleozoic to Mesozoic marine sedimentary and volcanic rocks, including the Guye Formation. This intense thermal contact recrystallized limestone layers into marbles and calcareous skarns, while subsequent silica-rich hydrothermal fluids filled open fractures and solution cavities with large quartz vugs. These pocket horizons are noted for producing deep purple amethyst scepters, Japan-law twinned quartz crystals, and sharp crystals of grossular garnet and magnetite. Mining and prospecting activity at the site began around the late nineteenth century with small-scale exploratory tunneling for iron ore, but shifted entirely to mineral specimen recovery by the mid-twentieth century. Organized field collecting and seasonal specimen mining peaked between the 1960s and 1980s under various private claims, and the rugged, high-elevation locality continues to see sporadic, low-impact hand-mining by dedicated collectors.

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