 | near Port Ludlow, Jefferson County, Washington |
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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 Crescent Formation 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 exposed at this dormant quarry contain vesicles that show a complex history of sub-greenschist facies (zeolite) mineralization. Mineralization is most prevalent directly above contacts between individual flows. This locality is listed in a mineral collecting pamphlet issued by the Washington State Mineral Council. Access may be subject to change.
MINERALS (incomplete list) CLICK for COMPLETE LIST
| CaCO3 - Occurs as fluorescent colorless, white to vibrant yellow crystals in a variety of habits within amygdules. | |||||
| Fe endmember chlorite - (Fe,Mg)3Fe3(Si,Al)4O10(OH)8 - Some amygdules are lined with fine-grained dark green to black platy masses. | |||||
| Cu - Occurs as mm-scale specimens including wire forms and individual crystals. | |||||
(Ca,Na2,K2)Al2Si4O12·6H2O
- Occurs as rare mm-scale milky white hexagonal plates (some with red/orange iron-oxide inclusions, pers. comm., John Cornish).
| SiO2
- Occurs as druses and microcrystalline dark green jasper. Some quartz druse clusters occur as spheres, some of which are aesthetically perched on clinochlore.
| NaCa2Al5Si13O36 . 16H2O
- Small colorless crystals line some amygdules.
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* photographed
CALCITE |
Drusy QUARTZ spheres on ropy CLINOCHLORE |
STILBITE, vesicle filling in basalt |
Drusy QUARTZ, light green JASPER |
LEVYNE |
COPPER wire on CLINOCHLORE |
CALCITE on CLINOCHLORE |
CONTACT me if you can help me identify these minerals
Unidentified #1 PHACOLITE? |
Unidentified #2 |
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.
