R. A. Gulbrandsen 1974 <p>Buddingtonite is distributed widely in the rocks of the Meade Peak Member of the Phosphoria Formation in southeastern Idaho and occurs in amounts up to about 50 percent. Most of the buddingtonite is in the middle mudstone interval of the member between two phosphate-rich intervals. The composition of the buddingtonite, in terms of a buddingtonite K-feldspar series, shows an apparent range of Bd₈₂KF₁₈ to Bd₁₃KF₈₇, and compositions of Bd₇₂KF₂₈ to Bd₅₀KF₅₀ may be the most common. The predominant silicate mineral suite consists of buddingtonite-albite-illite. Albite is present in amounts up to about 20 percent. Buddingtonite may have developed directly from volcanic glass in the presence of abundant ammonium, derived from the decomposition of organic matter, in interstitial waters, or it may have formed at some later diagenetic stage from other products of volcanic glass alteration, such as montmorillonite or zeolites.</p> application/pdf en U.S. Geological Survey Buddingtonite, ammonium feldspar, in the Phosphoria Formation, southeastern Idaho article