monazite

Monazite is a group of reddish-brown phosphate minerals that are important sources of rare earth elements. Its general formula is (REE)PO4, with the REE site commonly occupied by cerium, lanthanum, neodymium, and praseodymium. The minerals are often labeled as monazite-(Ce), monazite-(La), and monazite-(Nd) depending on the dominant rare earth. Thorium and, less commonly, uranium can substitute within the crystal structure, giving some samples radiological significance.

Monazite occurs in a variety of geological environments. It forms in igneous and metamorphic rocks, notably pegmatites and peraluminous granites, and can be concentrated in sedimentary heavy mineral sands by weathering and transport. These placer deposits are mined in coastal and inland settings around the world, including regions in India, Africa, Brazil, and Australia, where monazite is often recovered with other heavy minerals such as ilmenite, rutile, and zircon.

In hand specimen, monazite is typically brown to reddish-brown with a resinous to sub-metallic luster. It has a Mohs hardness of about 5–5.5 and a relatively high density. The mineral crystallizes in the monoclinic system and commonly occurs as prismatic or tabular grains, though it is frequently found as small grains in rocks and sediments.

Economically, monazite is a principal source of light and some heavy rare earth elements. Extraction involves crushing and concentrating the ore, followed by chemical processing to separate the REEs via acid digestion and solvent extraction. The thorium content necessitates radiological handling and regulatory considerations during mining and processing.