Hi Ilia
Theoretically you completely right, however, I took some of this sand to the laboratory for a check. I took it about 3 miles away from the beach with the faint hope that the millions of years that it was lying in the free air washed by seasonal rains free it from salt and bring it back to its original state. The most important thing that I have learned from my Italians tutors was to look for and adopt local materials. I keep trying. Sometimes it works and sometimes not. By the way, the land over hear, all of it, was covered by sea, geologycally not long time ago. So let see what the results be.