A few days ago — after recovering from an average long work stint by relaxing, walking, visiting, helping to lay flooring, and running errands while at the lake, then returning to our little house via Costco and a family meal or two in the big city we sometimes drive through — I wrote a note in an irregularly kept journal indicating that I had been dreaming about diopside skarn and actinolite schist. I understand dreaming about the former: skarns have been invading my territory at work recently, and diopside skarn is one of my favorite types of skarn, introduced to me way back when on the west side of the Inyo Mountains, somewhere near Big Pine, CA. I'm not sure why actinolite schist would pop into my dreaming mind; I haven't worked in those kinds of schists much before. Blueschists yeah, greenschists not so much.
I realized, looking through a batch of rocks lying about our little house, brought from here and there, often from mine dumps, sometimes from close by, other times from places as far away as northeastern Idaho or southcentral Alaska, that I have photos of what I was calling actinolite skarn, but which may really be tremolite skarn. I think the difference might only be apparent by either doing petrography or x-ray work, neither of which will be done on these rocks anytime soon.
So, on with the photos!
The tremolite-actinolite in this skarn is a pale yellowish green, a color my camera seems to want to either distort with too much green, too much blue, or not enough color at all.
The skarn is cut by numerous quartz-calcite veinlets containing pyrite, magnetite, and chalcopyrite. The veinlets are up to a half centimeter wide, usually more like a millimeter in width. Tiny.
The gray, vaguely bluish metallic mineral in the central part of the veinlet is magnetite. The brownish to yellowish mass of sulfides is mostly made of pyirte — you can barely make out a few cubic forms. Some of the shiny golden yellow grains are chalcopyrite. It's hard to say what the pyrite:chalcopyrite ratio is, even when looking at this rock in person.
This photo, especially when enlarged, shows the generally felted look of the fine-grained tremolite-actinolite.
Zooming in a bit, we can see the sheaf-like to radiating crystals of tremolite-actinolite, which are hosted in nearly invisible calcite and are possibly intergrown with other very fine-grained skarn minerals such as wollastonite.
A couple of the larger tremolite-actinolite crystals can be seen near the center of the way zoomed in photo above. The largest of these elongate sheaves is probably no more than a millimeter in length. Fine-grained indeed!
Actinolite is the iron-rich end member of the tremolite-actinolite series. I suspect that these very pale green to white crystals are tremolite. In hand sample, I usually just go by color, prefering my tremolite to be white to clear, but it can be light green, light yellow, brown, and even pinkish.
UPDATE: I've indicated the general area of where I most likely found this skarn rock in the Location shown below.