> it's prohibitively expensive to ship both the components and the finalized mixture to different areas.

We could do this if it is important. There are mines in Wisconsin the export sand to the middle east because that is known to work well for fracking and they don't want to risk a local sand not working well. (AFAIK they have never tested local sand properties, but it is possible they have and it doesn't work). In this case the value of the "perfect" is well worth the high shipping costs.

We certainly could - it's absolutely possible. The question is if it's economical and so far the market has ruled in most cases that it isn't. Either the project doesn't need such a perfect amalgamation of materials (maybe there is an expected deprecation that doesn't justify such an outlay - possibly earthquake risk would minimize any expected lifespan gain - possibly the materials contractor just can't internally justify the added material cost while remaining attractive to local contractors).

It's all a balance. Imagine a scenario where you can ship in specialized materials to build a bridge with an expected lifespan of 100 years and it'll cost 50M - or you could use local concrete that has an expected lifespan of 15 years and materials would cost 5M. This is a vast simplification of the math but, assuming those expected costs it'd be cheaper to build using local materials and just schedule replacement every 15 years. And, of course, there'll be egg on your face if you build the 50M bridge and then suffer a massive tsunami in two years that destroys the foundations anyways.

To paraphrase a Grady quote: "Engineering isn't a study of building the best thing - it's optimizing the quality we can get for the cost outlay."

for fracking, what they want is a perfectly uniform sized quartz grain thats rounded. You find this sand where multiple processes occur, notably glacial geology. You want uniform grains because frackings goal is to open, then support an porous structure when you can then pull the fluids/gas out without clogging.

It's not really hard to test for this property, but the cost efficiency is notable when you find a massive amount of it in one place. It still may be washed to remove further silt/clay, but they absolutely know the product works and they generally know the geology in other places don't tend to produce the same material.

There's a fair amount of materials size thats mostly "we found this geologic material and this is some magic shit" rather than some wholly manufactured human endevour.