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The monazite Mineral Group
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Monazite describes a group of several closely related phosphates with a varying range of several rare earth elements. Due to the similarity and indistinguishable visual differences of the members, a distinction between the Monazite types are rarely designated, with specimens simply labelled as Monazite. Monazite-(Ce), the cerium-rich end member, is by far the most common group mineral of this series, and accounts for most of the known specimens and occurrences.
Monazite is radioactive, and specimens may be metamict with rounded crystal faces. It is named for the Greek work "monazein", meaning alone, alluding to isolated crystals of the original occurrences of this mineral. |
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Chemical Formula |
General Group Formula of Common Members: (Ce,La,Nd)PO4
The most common members are:
Monazite-(Ce): (Ce,La,Nd)PO4
Monazite-(La): (La,Ce,Nd)PO4 Monazite-(Nd): (Nd,La,Ce)PO4 |
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Composition |
A rare earth phosphate, most often dominated by cerium, but also with lanthanum and neodymium. May also contain yttrium, thorium, and uranium. |
| Variable Formula |
(Ce,La,Nd,Y,Th,U)PO4 |
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Color |
Brown, reddish brown, yellowish-brown, yellow, orange, pink |
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Streak |
White |
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Hardness |
5 - 5.5 |
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Crystal System |
Monoclinic |
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Crystal Forms
and Aggregates |
In prismatic and tablular crystals, sometimes in fat stubby form and with many crystals faces. Prismatic crystals often have distinctive wedge-shaped terminations. Crystals may also be pyramidal or have complex faces. Twinning is common, and habits include crosses and re-entrant crystals, sometimes in unique "x" shaped formations. Also in rosettes, grainy, massive, and as rounded waterworn pebbles. |
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Transparency |
Transparent to translucent |
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Specific Gravity |
4.6 - 5.7 |
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Luster |
Resinous |
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Cleavage |
2,2. May exhibit parting. |
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Fracture |
Conchoidal, Uneven |
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Tenacity |
Brittle |
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Other ID Marks |
Radioactive |
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In Group |
Phosphates; True Phosphates |
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Striking Features |
Radioactivity, heavy weight, and mode of occurrence. |
| Environment |
Granite pegmatites, metamorphosed gneiss and schists, hydrothermal tin veins, and placer deposits. |
| Rock Type |
Igneous, Sedimentary, Metamorphic |
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Popularity (1-4)
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3 |
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Prevalence (1-3)
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3 |
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Demand (1-3) |
1 |
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Monazite is an important ore of the rare earth metals cerium, lanthanum, yttrium, and thorium.
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Monazite is found worldwide, but large crystals in good form are not common. Large, sharp prismatic crystals come from several localities at Iveland, Aust-Agder, Norway. Large brown crystals resembling Zircon have been found in the Ambatofotsikely pegmatite, Fidirana, Antananarivo Province, Madagascar.
A remarkable find of Monazite is at the Siglo Veinte Mine, Llallagua, Potosí, Bolivia, where sherry colored Monazite crystals form in aesthetic formations with Quartz crystals. Exceptional twinned crystals, in X-shaped twins, were found in Buenópolis and Diamantina, Minas Gerais, Brazil.
In the U.S., brown rounded Monazite has come from Trout Creek Pass, Chaffee Co., Colorado; and large crystals in loose soil from the Cactus Jack Pegmatite, Burnet Co., Texas. Sharp crystals have come from the Standpipe Hill Area, Topsham, Sagadahoc Co., Maine; and brown tabular crystals from Portland, Middlesex Co., Connecticut, at the Andrews (Hale), Case, and Strickland Quarries. Stubby crystals are found in the dumps of the Morefield Mine, Amelia Court House, Amelia Co., Virginia.
The above occurrences are primarily Monazite-(Ce), the most prevalent member of this group. Monazite-(La) has come from the Lovozero Massif, Murmanskaya Oblast', Northern Region, Russia; and Monazite-(Nd) from Monte Giove, Ossola Valley area, Piedmont, Italy.
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Zircon - Heavier, crystals may differ.
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