I broke open some quartz and noticed this white powder inside. There was a garlic smell when I cracked open the quartz. I was wondering if the powder could be arsenopyrite and if so could it be associated with gold deposition? Any thoughts?
It could be Arsenopyrite. It's hard to tell by the blurry pictures but the odor is right.
It looks more like serpentine or another hydrated silicate rather than quartz. If you are in the Sierra (Jamestown?) and it is serpentine you might have found another arsenic salt Cobalitite.
Arsenic minerals are sometimes found associated with gold but Arsenic is much more common than gold. Gold is where you find it. You will need to actually find gold to know if it's associated with the Arsenic mineral you have found. Good luck!