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The monazite Mineral Group

Well Crystallized Monazite Crystal

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.

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

Color

Brown, reddish brown, yellowish-brown, yellow, orange, pink

Crystal System

Monoclinic

Properties

Streak
White

Hardness
5 - 5.5

Transparency
Transparent to translucent

Specific Gravity
4.6 - 5.7

Luster
Resinous

Cleavage
2,2. May exhibit parting.

Fracture
Conchoidal, Uneven

Tenacity
Brittle

Other ID Marks
Radioactive

Crystal Habits

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.

3D Crystal Atlas

Additional Information

Composition
A rare earth phosphate, most often dominated by cerium, but also with lanthanum and neodymium. May also contain yttrium, thorium, and uranium.

In Group
Phosphates; True Phosphates

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

Uses

Monazite is an important ore of the rare earth metals cerium, lanthanum, yttrium, and thorium.

Noteworthy Localities

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.