This month's Accretionary Wedge is being hosted by the two co-bloggers at Highly Allochthonous, and it's a geo-image bonanza!
This rock is from a quartz vein in northern Nevada. Native gold (more properly electrum, a natural alloy of gold and silver) and the dark blue silver mineral naumannite are set in a matrix of clay-rich quartz. I wetted the specimen with water to enhance the visibility of the gold. The pen used for scale is the tip of an Ultra Fine Point Sharpie. The metal part of the tip is almost exactly 1mm across. The gold in this vein is not as yellow as some gold because of the silver content; the clay is not pinkish the way the photo makes it appear.
I'll be off to see some volcanic-hosted epithermal gold deposits in central Nevada this morning. Doubt if I'll see anything as gaudy as this, but maybe...
Accretionary Wedge #25: An Illustrated Glossary of Cool Geological Things