We have had this creek picked out for about six weeks but when we were here last the humidity was about 10% and the temps were in the mid 90's , perfect fire weather. We could not find a place to park where the trucks catalytic converter was not touching dry grass so we decided to come back later. A low is coming in from the ocean so the humidity was up to about 50% and I brought and old fashioned weed whip to cut the grass.One arm for the crutch and one for the weed whip got the job done.
I had found a piece of jade in the creek in the few minutes we were there last time so I had high expectations. The creek is very steep with many chest high water falls to be negotiated.After surmounting the first one we found huge amounts of blueschist which was very exciting. Blueschist is formed when undersea basalt is subducted and experiences an odd metamorphism. Blueschist facies metamorphism means that the rock was subjected to very high pressures , 7,000 to 9,000 times air pressure at sea level in this case but with temperatures not exceeding 400 degrees C. Since pressure is virtually instantaneous we have to assume there are conditions where temperature is not at the depth required for the relevant pressure . Rock is a good insulator , excellent really, and a wedge of rock can go down in the subduction trench and only have the interior get to 400C if it goes down very fast and emerges very fast as well. We are talking about 26 kilometers ( a kilometer is about 6 tenths of a mile) to get to the required pressure. Why is blueschist exciting? It is often very beautiful , blue and chatoyant , but it is too soft for lapidary purposes. It is however associated very strongly with jadeite and it has been found in a few places within ten miles of this creek.
