The reason I raise it, the more frequently travelled dirt roads are maintained with a thick layer of grey gravel. In this part of the world, that means dumping loads of this stuff onto the road every other week.
It is helluva treacherous and akin to riding on marbles. If there's been rain it beds down a little better, but otherwise it is very loose and the bike moves a lot. This isn't a big deal over short stretches but when you're looking at hundreds of kilos it's hard to remain focused. There is nothing worse than belting down a dirt road at speed only to see a fresh patch of thick grey gravel. It grabs your front wheel and it's a job keeping things together.
It's similar to your grey building gravel only rounder pebbles. If you feel the front wheel slip invariably you give a little gas and hope for the best. Nerve wracking when you're in a corner. This got me thinking about tyre combinations when someone remarked that I should dump the OEM tyres fast and look at a tyre mullet to help the front wheel track better. Turns out a lot of guys do it if they travel on a lot of gravel or are aggressive dirt bike riders.