The Composition and Distribution of Nodular Monazite in the Marvast Upper Triassic Shales (Yazd-Iran)

Millimetric, lens like and flat cake like monazite nodules are found within the Upper Triassic sedimentary rocks in Marvast in the south of Yazd. Monazite is one of the several rare earth phosphate minerals. Marvast monazite has a chemical formula of (Ce, La, Nd, Eu) PO4. The size of grains changes from 0.1 to 2mm and the grains with a diameter of 0.3-0.8 mm are often prevail. Monazite nodules are gray and greenish-gray in color and often formed in earthy aggregates. Monazite has a numerous inclusions of light minerals (such as quartz, calcite and. ..) and is enriched in Light and Middle Rare Earth Elements (LREE & MREE). Marvast monazite is completely different from igneous type Monazites. The nodules are formed during diagenesis of the Upper Triassic- Lower Jurassic sedimentary sequences and exposed in the shales. These nodules are potentially useful means for dating the diagenetic duration of the Upper Triassic sedimentary rocks.