Quartz-on-rock

As I said, these are rare structures. But I found three on Wilderness Hill in Littleton. Here are two others. Two views of one:
Two views of another found close to this above one:
Note that this one is placed in line with the split in a "spirit door". Taking into account the idea that a quartz-on-rock would function to project energy outward, a speculation about this structure is that it functioned to amplify what came out of the split.