Minerals of Port Ludlow Area Quarry, Jefferson County, Washington, USA

PORT LUDLOW AREA QUARRIES
near Port Ludlow, Jefferson County, Washington, USA

GEOLOGY
Crescent Formation - Late Paleocene to middle Eocene (62-48 Ma). The Crescent Formation is comprised of a large volume of submarine/subaerial basalt. The Crescent basalts are among the oldest basalts in this region and makeup the basement of the Coastal range. Babcock et al. (1992) concluded that the basalts erupted into a subsiding rift basin along the western coast approximately 60 mya. Exposure of the Crescent formation can be found as a continuous swath defining the northern, eastern, and southeastern edge of the Olympic Peninsula. Based on gravity studies, the Crescent Formation is thought to extend eastward beneath the Puget Sound to Seattle. Most of the Crescent Formation, especially on its eastern edge, is covered with Quaternary glacial till deposits.

Multiple basalt flows dipping gently to the south are exposed at quarries within this region. The basalts have experienced low-grade (sub-greenshist) metamorphism, allowing for the growth of a number of zeolite species. Open-space mineralization is not prolific. Most vugs are found near the contact between individual flows. Contact quarry owner for information on collecting access.

MINERALS (incomplete list)


Calcite-	CaCO₃ - Occurs as opaque colorless to gemmy yellow rhombohedral crystals to several inches.
Laumontite-	CaAl₂Si₄O₁₂ . 4H₂O - Occurs as white to slightly pink slender monoclinic crystals up to 1". Crystals readily dehydrate to leonhardite when exposed at the surface.
Levyne-	(Na,Ca)₂(Al,Si)₉O₁₈ . H₂O - Personal communication - John Cornish
Stilbite-	NaCa₂Al₅Si₁₃O₃₆ . 16H₂O - Occurs as peach-colored and white crystals (two generations) typically less than 1" lining some amygdules.
Thomsonite-Ca-	NaCa₂Al₅Si₅O₂₀ . 6H₂O - Occurs as botryoidal/radiating sprays lining some amygdules.

Rhombohedral CALCITE
on dehydrated
LAUMONTITE
(LEONHARDITE)

Dehydrated
LAUMONTITE (LEONHARDITE)
on CALCITE

STILBITE and
dehydrated LAUMONTITE
(LEONHARDITE)

CALCITE and THOMSONITE-Ca

Radial, color-zoned
THOMSONITE-Ca

REFERENCES
Babcock R. S., Burmester R. F., Engebretson, D. C., Warnock A., Clark K. P. (1992) A rifted origin for the Crescent basalts and related rocks in the northern Coast Range volcanic province, Washington and British Columbia. Journal of Geophysical Research, B, Solid Earth and Planets 97;5, 6799-6821.