325 onward in the sandy soil. This indicates good Mg availability from the fresh mafic rock to the plants. Figure 5 – Comparison of chemical soil attributes in Red Oxisol (Latossolo Vermelho, LV) and Quartzarenic Neosol (NQ) under increasing doses of fresh mafic rock and a reference limestone dose, incubated for 90 days under greenhouse conditions. (A) pH in water; (B) exchangeable Al; (C) exchangeable Ca; (D) exchangeable Mg; (E) sum of bases; (F) base saturation. The agronomic behavior of rock powders is strongly controlled by mineralogy, texture, and the intensity of alteration. In the Serra Norte mine (Carajás Mineral Province), mafic rocks affected by potassic hydrothermal alteration contain abundant K-bearing phases (K-feldspar and biotite/muscovite) and reactive Ca–Mg carriers such as calcite, amphiboles (actinolite–tremolite series), epidote and plagioclase, alongside Mg-rich chlorite. When finely ground, carbonate dissolution and the weathering of Ca–Mg silicates consume acidity and release Ca²⁺ and Mg²⁺,
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