“3 inch minus”

Interestingly, it seems that different localities tend to use different jargon for stone sizing, with not much standardization. There is no government agency that regulates it. :)

Regardless, since the sources of stone tend to use sieves with defined size holes to sort the stone, this tends to tell you the size of the stone to use. So around here, #3 stone means that which will fit through a sieve with 3 inch holes. In some cases, the stone will already have been run past smaller sieves.

I will suggest that stone with dirt in it will tend to support the growth of weeds, encourage tree roots more, etc. And since these stones tend to be more round, with few sharp edges, they don't really pack that well for a driveway base.

I have also seen that "crusher run" tends to pack very solidly. This is crushed limestone, run through the same sieves to size the stone. The sharp edges of crushed stone prevent things from sliding around, and the presence of smaller crushed stone fills in the interstices, locking things together even more. In fact, #3 crusher run seems to be a common base for driveways around here, with smaller sized crusher run on top as a surface. Our gravel driveway is made of exactly that.

So I would not be at all surprised if the heavy equipment guy was in fact referring to #3 crushed limestone for a base.