Summary: Brushite occurs as radial-concentric layers of prismatic crystals deposited on baked pellets of bentonite impregnated with cobalt oxide, placed in the reticulo-rumen of lambs as a preventive of cobalt-deficiency diseases. Collophane-like whitlockite, apparently pseudormorphous after brushite, occurs underneath the brushite layers, and struvite is found as rare minute crystals between the whitlockite and brnshite layers. Analytical and physical data are given for the first two minerals and the origin of the deposit is discussed.