To make any significant change in your clayey soil you would need tons of that stone dust and then, aside from maybe opening up the pore spaces, you would not have a better soil unless you also added copious quantities of organic matter which will do more to make that clayey soil better than all the stone dust you can find.

Thanks, kimmsr. I'm planning to add plenty of organic matter as well.

I'd like to focus on the value of stone dust itself. Does anyone know specifically whether it will "open up the pore spaces" or otherwise improve the tilth, drainage, mineral content, nutrient availability, etc. of the soil? Are the particle sizes too large or too small to be suitable? Since stone dust is a byproduct, is it generally clean? How does it compare with sand as a way to improve the non-"organic" component of the soil?

Does anyone know specifically whether it will "open up the pore spaces" or otherwise improve the tilth, drainage, mineral content, nutrient availability, etc. of the soil? Are the particle sizes too large or too small to be suitable?

It depends upon what type of stone (presume granite up there) and the particle size. It likely will add minerals and possibly improve Cation Exchange Capacity. Depending upon the ratio of addition, unless you add a ton probably won't do much for drainage. But just for mineral content and CEC, ISTM it is a net positive if the particle size is that of loam or larger. OM will improive tilth.

Dan

Dust won't open clay at all. It will make things worse than they are. Use compost instead, at least 2 inches of it.

Jean, is that because the particle sizes are too small, or is there something else about this material that wouldn't mix well with clay-ey soil and organic matter (compost)?

There is an old myth, one that I subscribed to for years, that adding sand, stone dust, to clay soils would give you an adobe like soil. However, according to the instructions on making Adobe from the University of New Mexico that is not how to make Adobe. Adding the stone dust to your clay soil would be like adding any other type of sand, or granite dust which is stone dust, or rock phosphate which is stone dust, or limestone which is rock dust, or greensand which is also a rock dust.
Depending on the source of that stone dust and how much baterial activity your soil has that stone dust could provide some type of necesssary macro and micro nutrients.