re: About filaments on "bounce" rock.
The filamentous features are rather subtle. I've attached some selected portions of the large image that focuses on the features I mean, but even here they are rather difficult to see.
The first two images appear to be of filamentous structures intrinsic to the rock. They have the appearance of a greyish biofilm or biofabric.
The third image appears to be of a single, individual strand similar to the bright strands suggested by NASA to be Vectran threads. It is bright white, about in the center of the image, oriented diagonally.
Bob Clark