[unlikelymordant]

This whole 'undesireable side reactions' thing is completely overblown for basalts. The effects to soil of volcanic ash from eruptions is quite well studied, not to mention crushed basalt is a recognised fertiliser in organic and biodynamic farming, and there have been places spreading it each year for the last 40 years (purely as a fertliser). You cant use rocks with significant sulphides or other heavy metals though, that has to be tested before spreading. Basalt is quite wide spread.