Minerals of the Skookumchuck Dam area, Thurston County, Washington, USA

Skookumchuck Dam
Bucoda, Thurston County, Washington, USA

LOCALITY IMAGES

GEOLOGY
Northcraft Formation - Eocene (50-42 Ma). Eocene basalt flows containing sizable zeolite pockets were encountered duing blasting for the dam abutment and spillway along the north and south sides of the Skookumchuck River valley between 1969 and 1971. Most specimens were collected by the project geologist during construction (Charles Trantham), Rudy Tschernich and the dam guard. Large mesolite crystals, pink to orange heulandite clusters and exceptional analcime specimens are the notable species collected at this time. No collecting is permitted.

MINERALS

Analcime-	NaAlSi₂O₆ . H₂O
Calcite-	CaCO₃
*Mordenite-	(Na₂,Ca,K₂)Al₂Si₁₀O₂₄ - 7H₂O
*Heulandite-	(Ca,Na)_2-3Al₃(Al,Si)₂Si₁₃O₃₆ . 12H₂O
Stilbite-	NaCa₂Al₅Si₁₃O₃₆ . 16H₂O

* photographed

pink HEULANDITE on MORDENITE	pink HEULANDITE	pink HEULANDITE
	STILBITE "bow tie"

REFERENCES
mindat.org (https://www.mindat.org/loc-15519.html)