Growth of world population and consequent growth of food demand are drivers of expansion and intensification of agriculture. High-yield agriculture relies on fertilizers that, therefore, become a key focus to address concerns on global food security. Currently, potassium fertilizers are produced in the northern hemisphere. These fertilizers do not suit the deep leached soils of tropical countries, partly due to their high solubility. The use of geological materials (agrominerals) such as K-bearing silicates could be an option to develop slow release potassium fertilizers from abundant and readily available geologic sources. Thus far, both laboratory and agronomic field tests on such materials have been inconclusive, meaning that a clear relationship between the application of agrominerals to soil and the fertilizing effect could not be established. Novel interdisciplinary approaches are needed to predict the release of nutrients from agrominerals. This study presents one such approach, proposing a detailed analysis of the relationship between petrographic characteristics of twelve samples of ultrapotassic syenite (K-feldspar ore), and the leaching of potassium from their powders. The correlation between petrographic features, comminution and leaching proposed here, is expected to play a major role in the assessment of the fertilizing properties of agrominerals in the field. (C) 2016 Elsevier Ltd. All rights reserved.