If you open the article and click the only link in the first paragraph, leading to the source, it will tell you in the introduction > Crushed metabasalt and ol

If you open the article and click the only link in the first paragraph, leading to the source, it will tell you in the introduction > Crushed metabasalt and olivine soil amendments were used to investigate changes in soil pore water alkalinity as a proxy for bicarbonate production. The metabasalt (median grain size: 102 ± 22 μm) was selected because of its benign elemental composition and modest weathering potential (the parent volcanics includes felsic facies, yielding an overall silica content in the intermediate-to-felsic range). The olivine (median grain size: 83 ± 12 μm), in contrast, was chosen for its potential to weather rapidly TL;DR scan for the digits in that quote. This stuff is measured in micrometers. > Why would you even study such things? Because if everyone were willing to read sources and get to understandings, we would probably not have climate problems in the first place