Monazite yellow or brown rare earth phosphate monoclinic (small crystals flattened { 100}, also as detrital grains) mineral with appreciable substitution of thorium for rare earth and silicon for phosphorus. It is the principal ore of the rare earths and of thorium. Its cleavage is distinct {100}; parting on {001}; hardness is 5-5.5 on Moh's scale and specific gravity is 4.6-5.4. It occurs as an accessory mineral in acid igneous rocks, in pegmatite dykes and in detrital sands and sandstones. It is also known as cryptolite.

In Bangladesh monazite is found as beach sand heavy mineral placer deposits in the sea beaches and coastal islands of Cox's Bazar, and the districts of Chittagong, Noakhali and Patuakhali. It occurs mostly with fine to very fine sand. Generally the sands containing it are even finer than the sands containing ilmenite, garnet and rutile. The highest concentration of monazite is reported from Badarmokam as 1.2%, the lowest concentration from Kuakata as 0.01% and the average is 0.31%. The total reserve of monazite in Bangladesh is 17,352 thousand ton. [Sifatul Quader Chowdhury]