Although these particles are larger than the crushed material, they are held together by a water soluble compound that quickly breaks down in the soil. Pelletized fertilizers are less dusty and easier to use, but more expensive. If you add rock mineral fertilizers to your soil, it is important to add organic matter as well. Organic matter helps stabilize the soil pH, which, in turn, increases microorganism activity. Microorganisms are key to breaking down the rock mineral fertilizers to usable form for the plant.
Sulfur Apply in late spring or summer to lower pH of alkaline soils.
Sulfur is mined in the western U.S., but most is a by-product of oil refining. Epsom Salt Apply at planting time or during the growing season to supply magnesium and sulfate. It's fast-acting, but benefits last 1 or 2 growing seasons. Epsom salt is mined in Europe, but most that is available to gardeners is manufactured. Dolomitic Limestone Apply in fall to raise pH of acidic soils that contain insufficient magnesium.