Hypothesis: Amorphous Magnesium-Calcium Phosphate (AMCP) particles in the distal small intestine have been shown to have a fundamental role in mammals' immune-surveillance mechanisms. Their formation in the gut lumen and their stability against crystallization are expected to depend upon physiological conditions such as pH and [Mg2+]. Knowing the influence of these parameters on AMCP stability would allow to predict the presence and the activity of the particles in physiological or pathological conditions. Experiments: We performed the synthesis of AMCP particles at physiological temperature, in phosphate buffer at variable pH from similar to 7.0 to 7.4. The stability of the particles was then tested by dispersing them in different conditions of [Mg2+], pH and concentration, so to mimic different biological conditions. The particles were characterized in terms of morphology, crystallinity, chemical composition and porosity. Findings: The characterization showed that we managed to prepare AMCPs with features matching those of the endogenous particles. Both the lifetime of the amorphous phase and the nature of the formed crystalline material were found to depend upon [Mg2+], pH and concentration. This article paves the way for the comprehension of possible dysfunctions of the gut immune-surveillance mechanisms due to imbalances of these physico-chemical parameters. (C) 2018 Elsevier Inc. All rights reserved.