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Monazite
Current inventory:  0 gems
 

Chemistry:  (Ce,La,Nd,Th)PO₄  [Cerium Lanthanum Neodymium Thorium Phosphate]

Discovered in 1829;   IMA status: Valid (pre-IMA; Grandfathered).
Monazite is named from the Greek word monazein, meaning to be solitary because of the rarity of the mineral in the first known localities, plus "Ce" as the cerium dominant member of the Monazite Series.

Classification

Mineral Classification:

Phosphates

Strunz 8th Ed. ID:

7/A.15-20

Nickel-Strunz 10th Ed. ID:

8.AD.50

8 : PHOSPHATES, ARSENATES, VANADATES
A : Phosphates, etc. without additional anions, without H₂O
D : With only large cations

Related to:

Monazite Group: Monazite-(La), Monazite-(Ce), Monazite-(Nd), Monazite-(Sm), Cheralite-(Ce), Brabantite

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Crystals typically tabular on [100], may be prismatic, equant or wedge-shaped, to 27 cm; granular, massive.

Twinning:

Common, [100] as twin and composition plane, as contact twins.

Physical Properties

Cleavage:

[100] Distinct, [010] Poor; parting on [001] or [111]

Fracture:

Conchoidal to Irregular/Uneven

Tenacity:

Brittle

Hardness (Mohs):

5.0 - 5.5

Density:

4.98 - 5.43 (g/cm³)

Luminescence:

Dull brown cathodluminescence

Radioactivity:

If rich in Thorium: Weak; GRapi = 91,584.19 (Gamma Ray American Petroleum Institute Units)

Other:

Metamict if rich in Thorium. Paramagnetic

Optical Properties

Color:

Reddish Brown, Brown, pale Yellow, Pink, Grayish White

Transparency:

Translucent to Opaque

Luster:

Vitreous to Sub-Adamantine, Resinous, Waxy

Refractive Index:

1.770 - 1.860 Biaxial (+)

Birefringence:

0.053 - 0.067

Dispersion:

 r < v  or  r > v, weak, horizontal

Pleochroism:

Weak; Faint to imperceptible. In pale yellows.

Occurances

Geological Setting:

An accessory mineral in granites, syenites, and their pegmatites; in carbonatites and volcanoclastic rocks; in fissure veins and high-grade metamorphic rocks; commonly detrital in river and beach sands; rarely authigenic in shales and intense weathering zones.

Common Associations:

Allanite, Columbite, Thorite, Titanite, Wolframite, Xenotime, Zircon (pegmatites and Alpine fissures); Cerianite, Churchite, Florencite, Rhabdophane (Mt. Weld, Australia).

Type Locality:

Ilmen Natural Reserve, Ilmen Mts, Chelyabinsk Oblast', Southern Urals, Urals Region, Russia

Year Discovered:

1829

View mineral photos:

Monazite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Monazite is a very rare gem that is slightly radioactive as defined in 49 CFR 173.403 (greater than 70 Bq/gram) due to the presence of Thorium (Th). Facetable material is very rare as most Monazite is a dull and opaque brown. Faceted gems are usually very small but an intense reddish brown.

Monazite is a primary ore of several rare earth elements (REE) such as Thorium, Cerium and Lanthanum. Thorium is highly radioactive. Since Monazite is radioactive it is often metamict. Metamict is the condition when the radiation destroys the crystal lattice completely while leaving the outward appearance of the crystal unchanged. Increased metamictation will increase the transformation of the mineral's fracture from irregular/uneven to conchoidal.

Monazite is widely distributed but gem quality crystals are quite rare. The main sources of gems are Minas Gerais, Brazil and Tsumeb, Namibia.
 

  
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