[Fiction question] I need a rock collector or geologist now. Can you just find a chunk of beryl or quartz lying around on the ground?

Let’s say you’re in a meadow in the Concord, NH, area. This piece of land has never been cultivated, being rather rocky and hilly, but it abuts farmlands. At the upper end of the clearing there is a large granite outcropping at the edge of the woods. Not far from the outcropping, a shallow grave was recently dug. You are an experienced rock collector, and you are walking up the sloping meadow toward the granite outcropping, passing near to the shallow grave. Could you happen to find a good-size chunk of collectible rock just lying there visible on the surface, or even just sticking up a little bit so that you could see it and dig it out?

If this would be a little bit of a stretch, but could still happen, please tell me it’ll work.

In that case, what kind of rock, and could it be a chunk big enough to serve as a weapon in a few more minutes?