PORT LUDLOW AREA QUARRIES
near Port Ludlow, Washington
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 - Opaque colorless to gemmy yellow rhombohedral crystals up to 8" long.
Laumontite-
CaAl2Si4O12 . 4H2O - 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 - White to tan crystals to 1" line some amygdules.
Thomsonite-
NaCa2Al5Si5O20 . 6H2O - Forms botryoidal/radiating sprays lining some amygdules.

Rhombohedral CALCITE
on dehydrated LAUMONTITE
(LEONHARDITE)

STILBITE

STILBITE and
dehydrated LAUMONTITE
(LEONHARDITE)





CALCITE and THOMSONITE

CALCITE and THOMSONITE



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.