Matching Leaf Imprint
The grain has a molded surface as shown by the notch on the lower left.
In Photoshop the image of the tip of the leaf just to the right of the grain was copied and pasted into the notch… it’s a perfect fit, a molded surface and the grain formed in moss.
The arrows indicate where strands of fungus from either side of the moss leaf enter the grain of silica. The fungus “transits” the entire length of the grain and exits from the other end. Presence of the fungus inside the moss as well as inside the grain demonstrates the grain formed right where we see it. Further, since this is the growing tip of the moss plant, the grain could not have formed long ago.