
home sweet home...
the spires are each in a 5x5 pit that goes down about 8 blocks.
for finding diamonds, it's all about covering a lot of ground. I build a series of hallways at every level of the staircase below 16. 20 out from the staircase, 16 right and left, and then 16 block hallways off of that, 2 blocks apart. one mine might yield about 5 diamonds, but provides more coal, iron, and redstone (cobblestone, too, obviously) than you'll ever want.