| Monazite | |
|---|---|
-164025.jpg) Monazite-(Ce) | |
| General | |
| Category | Phosphate minerals |
| Formula (repeating unit) | (Ce,La,Th)PO4 |
| Strunz classification | 8.AD.50 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H–M symbol) |
| Space group | P21/n |
| Identification | |
| Color | Orange, purple, reddish brown, brown, pale yellow, pink, blue, green, gray, |
| Crystal habit | Commonly as prismatic or wedge-shaped crystals |
| Twinning | Contact twins common |
| Cleavage | Distinct on [100] poor on [010] |
| Fracture | Conchoidal to uneven |
| Mohs scale hardness | 5.0–5.5 |
| Luster | Resinous, vitreous to adamantine |
| Streak | White |
| Diaphaneity | Translucent to opaque |
| Specific gravity | 4.6–5.7 (4.98–5.43 for monazite-Ce) |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.770–1.793 nβ = 1.778–1.800 nγ = 1.823–1.860 |
| Pleochroism | Weak |
| 2V angle | 10–26° |
| Melting point | 1900–2100 |
| Other characteristics |  Radioactive if uranium and/or thorium-rich, dull brown cathodoluminescence, paramagnetic |
| Magnetism | Paramagnetic, moderately strongly |
| References | [1][2] |
Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals.[3] The most common species of the group is monazite-(Ce), that is, the cerium-dominant member of the group.[4] It occurs usually in small isolated crystals. It has a hardness of 5.0 to 5.5 on the Mohs scale of mineral hardness and is relatively dense, about 4.6 to 5.7 g/cm3. There are five different most common species of monazite, depending on the relative amounts of the rare earth elements in the mineral:[5]
- monazite-(Ce), (Ce,La,Nd,Th)PO4 (the most common member),
- monazite-(La), (La,Ce,Nd)PO4,
- monazite-(Nd), (Nd,La,Ce)PO4,
- monazite-(Sm), (Sm,Gd,Ce,Th)PO4,
- monazite-(Pr), (Pr,Ce,Nd,Th)PO4.
The elements in parentheses are listed in the order of their relative proportion within the mineral: lanthanum is the most common rare-earth element in monazite-(La), and so forth. Silica (SiO2) is present in trace amounts, as well as small amounts of uranium and thorium. Due to the alpha decay of thorium and uranium, monazite contains a significant amount of helium, which can be extracted by heating.[6]
The following analyses are of monazite from: (I.) Burke County, North Carolina, US; (II.) Arendal, Norway; (III.) Emmaville, New South Wales, Australia.[7]
| I. | II. | III. | ||
| Phosphorus pentoxide (P2O5) | 29.28 | 27.55 | 25.09 | |
| Cerium oxide (Ce2O3) | 31.38 | 29.20 | 36.64 | |
| Lanthanum oxide (La2O3) Didymium oxide (Di2O3) |
30.88 | 26.26 | 30.21 | |
| Yttrium oxide (Y2O3) | — | 3.82 | — | |
| Thorium oxide (ThO2) | 6.49 | 9.57 | 1.23 | |
| Silica (SiO2) | 1.40 | 1.86 | 3.21 | |
| Alumina (Al2O3) | — | — | 3.11 | |
| Iron oxide (Fe2O3) | — | 1.13 | — | |
| Lime (CaO) | — | 0.69 | — | |
| Water (H2O) | 0.20 | 0.52 | — | |
| 99.63 | 100.60 | 99.49 | ||
| Specific gravity | 5.10 | 5.15 | 5.001 | |
Monazite is an important ore for thorium,[8] lanthanum, and cerium.[9] It is often found in placer deposits. India, Madagascar, and South Africa have large deposits of monazite sands. The deposits in India are particularly rich in monazite.
Monazite is radioactive due to the presence of thorium and, less commonly, uranium. The radiogenic decay of uranium and thorium to lead enables monazite to be dated through monazite geochronology. Monazite crystals often have multiple distinct zones that formed through successive geologic events that lead to monazite crystallization.[10] These domains can be dated to gain insight into the geologic history of its host rocks.
The name monazite comes from the Ancient Greek: μονάζειν, romanized: monázein (to be solitary), via German Monazit, in allusion to its isolated crystals.[11]
- ^ Mineralienatlas.
- ^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Monazite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved 23 July 2022.[permanent dead link]
- ^ Monazite group on Mindat.org
- ^ Monazite-(Ce) on Mindat.org
- ^ Monazite group on Mindat.org
- ^ "Helium From Sand", March 1931, Popular Mechanics p. 460.
- ^ Spencer, Leonard James (1911). . In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 18 (11th ed.). Cambridge University Press. p. 692.
- ^ Wolfgang Stoll "Thorium and Thorium Compounds" Ullmann's Encyclopedia of Industrial Chemistry 2012 Wiley-VCH, Weinheim. doi:10.1002/14356007.a27_001.
- ^ McGill, Ian (2005) "Rare Earth Elements" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a22_607.
- ^ Williams, Michael L.; Jercinovic, Michael J.; Hetherington, Callum J. (2007). "Microprobe Monazite Geochronology: Understanding Geologic Processes by Integrating Composition and Chronology". Annual Review of Earth and Planetary Sciences. 35 (1): 137–175. Bibcode:2007AREPS..35..137W. doi:10.1146/annurev.earth.35.031306.140228. ISSN 0084-6597.
- ^ Oxford English Dictionary, 3rd edition, 2002.