We didn't count, but indeed, black spots litter Waikiki's sidewalks. There are possible explanations:

The guys putting tar on nearby roofs didn't put down drop cloths.

Birds in the area have way too much iron in their diets.

But the most likely explanation is that it's chewing-gum fossils. Trace amounts of Wrigley's or Bazooka Joe attract dirt and then it catalyzes in the sun into a diamond-hard scab. Actually, dried chewing gum may be harder than diamonds. You couldn't get it off with pile drivers, acid, jackhammers or hot lava.

The only thing that works is freezing the stuff, which makes it frangible. In northern cities, gum freezes on the sidewalks in winter and chips up. But here, unless you want to pour liquid nitrogen over the sidewalk, forget it. It's not attractive, but once the chewiness goes away, it's not a hazard. Sometimes we think Singapore is on the right track by banning gum.

In a similar vein, it's that time of year when we get queries about translucent yellow spots appearing on cars. Actually, they appear everywhere, but people only notice them on cars. If you're thinking "bee poop" right now, you're a winner. Bees sometimes unload pollen-concentrated excess cargo while flying back to the hive.