The pH of crushed limestone that I have seen is around 8.0 something so your stone would be somewhere around the same.

Limestone is calcium carbonate- from which we get lime. Lime dust is... lime. Not quick, slaked, or hydraulic lime- just lime.

Do you have a normally acidic soil?

No my soil is alkaline clay (pH 7.6 according to a soil test I had done when seeding a new lawn) you can see gray limestone protruding from the ground all around my county (Rockingham county, Virginia.)

- Steve

As a geologist I'd have to know the asociate materials of the original limestone. A lot depends on the matrix (think of marble vs crumbly mortar). Probably a rating of anywhere of the high 7s to 8.6.

Remember, however, the 'dust' is not all soluble (marble vs mortar). Also, your rainwater is probably around 5.5 or even 5.3 and probably offsets any leaching out from the dust. The 'stuff' in the cracks, although sort of limey, might actually not be any more base or acidic than the surrounding soil.

You can sometimes speculate as to the ph of the soil by what weeds easily grow.