Heulandite

specimen number:
2282080

location:
Skookumchuck Dam, Thurston Co., Washington, USA

description:
Lustrous pinkish crystals of heulandite across the top of matrix. Collected by Chuck Trantham in 1969.

The Skookumchuck Dam, located on the Skookumchuck River in Thurston County, Washington, is a notable non-mining infrastructure locality highly regarded for its exceptional zeolite mineral specimens. Geologically, the site is positioned within the Eocene-aged Northcraft Formation, which features thick sequences of subaerial basalt flows and flow breccias. During the primary blasting and excavation of the dam abutment and spillway between 1969 and 1971, engineers breached extensive, gas-formed vesicular cavities and fractures within the volcanic bedrock. These open pockets were lined with diverse secondary minerals deposited by post-volcanic hydrothermal fluids, including mesolite needles, analcime, stilbite, mordenite, and heulandite. Because the locality was entirely exposed as a result of civil engineering construction rather than commercial mineral extraction, all specimen recovery was short-lived and restricted to the active construction window, and the completed dam facility remains strictly closed to any public entry or mineral collecting.

Charles "Chuck" Trantham was a prominent California field collector, mineral dealer, and professional geologist whose work significantly advanced the preservation of Pacific Northwest and California mineral specimens. Employed as the project geologist during the construction of the Skookumchuck Dam in the late 1960s and early 1970s, he recognized the mineralogical importance of the exposed zeolite pockets and actively salvaged many of the finest choice specimens before they could be destroyed by heavy construction machinery.

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