Monazite

Monazite is a phosphate of rare earth elements such as cerium, lanthanum and neodymium, and most specimens contain some thorium. It is a heavy, reddish-brown mineral with a resinous lustre. It occurs as small crystals in rocks such as granite, and because it is heavy and durable it collects in beach and river sands. Because of its thorium it can be radioactive, so it is not a stone to carry or wear.

Rare earth elements: Monazite is an ore of rare earths such as cerium, lanthanum and neodymium. According to the USGS, the largest use of rare earths worldwide is in magnets (neodymium magnets); in the United States the largest use is in catalysts. Thorium: Thorium, once used in gas lamp mantles, was obtained from monazite. Geological dating: The zones in its crystals make it possible to date events in the history of rocks.

It has a hardness of 5–5.5 on the Mohs scale. A fingernail cannot scratch it, but a steel knife can. Its specific gravity is 4.98–5.43 g/cm³.

Its best-known localities: Bayan Obo, Inner Mongolia, China; Mount Weld, Western Australia; Chavara, Kerala, India; Ilmen Mountains (Miass), Chelyabinsk, Russia; Steenkampskraal, Western Cape, South Africa.

Known localities in Türkiye: Kızılcaören, Beylikova, Eskişehir, Türkiye.

It is reddish brown, brown, yellowish or pinkish, with a lustre ranging from resinous and waxy to glassy or diamond-like. The streak (powder colour) is greyish white. Its hardness is 5–5.5 and its specific gravity about 5, so it feels heavy. Crystals are mostly flat tablets, sometimes wedge-shaped or prismatic, with a distinct cleavage in one direction. Thorium-rich specimens are radioactive and register on a radiation meter such as a Geiger counter. A sure identification needs laboratory analysis. Monazite has no widely known imitation. It can be confused with other heavy mineral grains in beach sands (such as zircon and xenotime); because they are hard to tell apart by eye, analysis is needed for a sure identification.

On the “street to diamond” value ladder it sits on step 4 of nine: Fine dimension stone and ore. Monazite is an ore, and its value depends on the proportion of rare earth oxides in it and which elements it holds (magnet elements such as neodymium and praseodymium are the most sought after), the cost and legal rules for managing radioactive components such as thorium and uranium, the size and type of the deposit (a by-product of beach sands, or a carbonatite) and demand from the magnet industry. Monazite is often recovered as a by-product of mining ilmenite, rutile and zircon, while thorium-poor bastnäsite deposits have to some extent pushed it into the background by easing radioactive waste concerns. For collectors, large, well-formed crystals count, but keeping and carrying radioactive specimens is subject to legal rules.

Some “negative ion” bracelets, necklaces and sleep masks deliberately contain naturally radioactive minerals such as monazite and zircon; these products are sold with claims that they improve circulation, stamina and energy, “detoxify” the body and prevent cancer. Hassan and colleagues (2021) examined 15 bracelets and 5 necklaces bought online; they found the products rich in monazite and zircon, some of them exceeding the public dose limit of 1 mSv a year when worn continuously (the highest sample reached about 1.22 mSv a year when worn 16 hours a day), and recommended banning the import and sale of such products. All 10 “negative ion” products examined by the Dutch RIVM in 2021 contained more radioactivity than the law allows. No health benefit has been shown for these products; monazite or other radioactive stones should not be worn on the body or put in water. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.

Monazite can be radioactive because of the thorium (and a little uranium) it contains. Keep specimens in a closed, labelled container in a well-ventilated place, away from bedrooms, kitchens and living areas and out of reach of children; do not carry one with you and do not hold it longer than necessary. Never break, grind or sand it: if the dust is breathed or swallowed, it irradiates the body from the inside. Do not wear monazite as jewellery, put it in water or put it in your mouth. Keeping, carrying and posting radioactive materials is subject to legal regulation in many countries; in Türkiye the competent authority is the Nuclear Regulatory Authority (NDK). Wash your hands after handling.