I have been doing a lot of digging in a thick murine clay as part of a construction project. In the course of doing this work, we noticed significant bands and streaks of blue color in the clay, which I know can be sign of silver.
Recently, we dug a hole using a hydrojet and noticed metallic flocculation in the froth. This flocculation is dark gray, but also has tiny flakes of silver color. On examining the flakes under a metallurgical microscope, they tend to have rounded edges and surfaces and have a silver-like luster, so that excludes mica.
We have exposed the material to a reducing flame but do not see much change either in the metallic element or the matrix, which is a murine silica clay.
Since silver rarely occurs natively, I am hesitant to identify it as silver, but nevertheless that creates the question of what it might be. One possibility is vivianite, an iron-phosphorous mineral, or perhaps arsenic.
Are there any easy tests that can be done to identify it as silver? I know I can do a bead test, but the bead test for silver is dark gray and we already have a dark gray flocculation, so I suspect that test would be positive. What's the next step?
(Please submit answers that I can do. Saying "send it to a lab" is obvious and I am already aware of that option.)
