The theme fo this month's accretionary wedge is Desk-crops. My favorite deskcrop is one I inherited when I took over my current classroom lab. Because I inherited it, I don't know much of its history although I will assume it was collected somewhat locally. Although it is one of my favorites now, I'll admit that for the first couple of months, I didn't really look at it; I thought it was another piece of basalt. Sure it had a nice blocky texture and vesicles, but in all, I just considered it another piece of basalt, like the kind we find all over around here.
But then, the former lab instructor started telling me about some of her favorite rock samples in the lab. She mentioned one with "lavacicles," so I got to looking for it, turned over this sample and there they were.
If you look at the right side of the block you can see the texture is much smoother, and the rock forms nice rounded surfaces, like drips frozen in time. I interpret this as once having been at or near the top of an old lava tube, the heat from a subsequent flow was sufficient to remelt a portion of the surface forming the lavacicles.
No comments:
Post a Comment