Understanding Rock Relationships in the Field During our fieldwork with my trainee geologist, we examined a large boulder that had been blasted from a lithium-bearing vein. Within the boulder, we observed three distinct rock materials -gneiss, muscovite pegmatite, and a lithium-rich pegmatite. By carefully studying their relationships, we identified the gneiss as the older host rock, followed by the mica (muscovite) pegmatite, and finally the lithium-bearing pegmatite, which represents a younger