Greenstone is a nonfoliated (minerals are not aligned) metamorphic rock. It begins its life cycle as basalt, a mafic (mostly magnesium & iron) igneous rock that makes up the ocean floor and Hawaii. After undergoing low-grade metamorphism (low heat and pressure) it becomes greenstone. To identify it look for a blah-looking green, greenish-gray, or nearly black, fine-grained rock. It is somewhat heavy due to the iron and magnesium that makes up many of the minerals.
In this area it may be brecciated and it may contain veins of white calcite. This rock was formed at a mid-ocean ridge, as basalt. After millions of years and miles of sediments being deposited on top of it, the entire stack of ocean floor goodies were scraped off the Farallon Plate, an oceanic lithospheric plate that was subducting under the North American Plate. During that process the basalt and sediments were metamorphosed by a process called “regional metamorphism”. A hundred million years, or so later, weathering, erosion, and Cal Trans or the Army Corps of Engineers exposed the rock at Earth’ surface.
I have a goal for 2014 of hiding caches on days when the month and date match. I hid one cache on 1/1, two caches on 2/2, and three caches on 3/3. With luck and hard work I can keep it up all year. This month was especially difficult because Dinosaur Day Science Fest was held on May the fourth. So, I have been super busy.
Remember, have fun and write a nice log.