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Monazite-(Ce) from
the Siglo XX mine,
Llallagua, Bolivia

Monazite gets its name from the Greek word "monazein", which means "to be alone", in allusion to its isolated crystals and their rarity when first found. Typically the various species of Monazite are found in granitic pegmatites, but recently, a remarkable discovery of some of the most vibrant and attractive crystals of Monazite was made at the historic and world famous Siglo XX mine in Llallagua, Bolivia. This mine is renowned for its phosphate species, and Monazite is among the most highly sought after among collectors. The crystals at Siglo XX are found in hydrothermal tin veins where there is almost a complete absence of Thorium (usually a trace element in Monazite).  This contributes to the brighter color of these crystals.  I have labeled these specimens as Monazite-(Ce), as I had a few specimens analyzed, and all of them came back with just a slight amount of Thorium present. It has been reported to me that certain pieces of this material show zero Thorium content whatsoever, and thus have been labeled as Monazite-(Nd). Without analyzing each individual specimen, one cannot be certain of the true identity of all the pieces in this update, so Im staying on the safe side and labeling them all as Monazite-(Ce).

Below is the entry for Monazite from Mark Chance Bandy's famous book, Mineralogy of Llallagua, Bolivia which was published in 1944, and is still very applicable to this day.


Copyright 1976 TGMS

These specimens represent the finest examples of the species that I have seen from this mine, and arguably any other mine due to the fact that they form in beautiful butterfly, heart or X-shaped twinned crystals (twinned on {100} and often interpenetrating), on gem quality Quartz crystal matrix. Typically, Monazite occurs in somber colors, i.e., brown, and are often opaque, whereas these crystals are translucent to gemmy and bright in appearance. Perhaps the most intriguing aspect of these specimen is that they exhibit an evident color change effect in different lighting. The hue of the crystals range from orange-pink in incandescent and sunlight, to a dull yellow or whitish-yellow color in certain fluorescent lighting and spiral energy saver bulbs. The change in color is very appealing, and we have illustrated this phenomena below as an example. **Please note that these specimens do not photograph exactly true to color, because the camera has great difficulty capturing the subtleties of the hues, so please keep this in mind when viewing the photos below.


(Above photos taken in sunlight)


(Above photos taken in under spiral,
mercury-bearing "energy saver" light bulbs)

Aside from Quartz, the only notable associated species with this material is Xenotime. These crystals are typically 1-2 mm, with a simple tetragonal prismatic habit, and also display a color change ranging from a pale greenish-yellow in incandescent and sunlight, but show a strong reddish-orange color under spiral energy saver bulbs. I have only ONE confirmed specimen in this lot with a Xenotime association, but that is not to say that other pieces might also have Xenotime crystals present which I could not see.

Lastly, it must be noted that Monazite is not often found in such well-crystallized display specimens as these new pieces from Siglo XX. It is often the case that Monazite crystals are found either embedded in matrix, or as single or floater crystals off matrix. The crystals on these specimens (some of which exceed 1 cm.) are certainly the largest I have seen from this locality, and the fact they are prominently sitting atop highly desirable Quartz crystal matrix and are not at all buried, makes them all the more attractive. This is a great opportunity for collectors to obtain an excellent Monazite specimen from one of the most storied localities in the world.

Enjoy !

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(click on highlighted picture to enlarge)

Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12081a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12081b.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12081c.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12081d.JPG]


No. MON 12081 - $ 2500.00

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 15.2 x 11.2 x 7.3 cm (large cabinet)
Largest crystal: 1.0 cm.


This the best large cabinet specimen of this material that I have seen. Possibly the best large cabinet Monazite from this mine extant. The piece is simply loaded with dozens upon dozens on superb quality, sharp, lustrous, translucent butterfly or X-shaped twinned crystals of pinkish-orange Monazite-(Ce) sitting atop gemmy, prismatic colorless Quartz crystals on matrix. Admittedly, the piece could use a trim, and the specimen honestly looks much better in person than the photos indicate. For the size of the piece, the quality of the crystals, and overall visual appeal, this is a significant phosphate specimen from any locality.

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Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12082a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12082b.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12082c.JPG]


No. MON 12082 - SOLD

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 7.3 x 4.8 x 3.2 cm (small cabinet)
Largest crystal: 0.5 cm.


A good reference piece featuring a few sharp, lustrous, gemmy, pinkish-orange color twinned crystals with gem/gemmy Quartz crystals on matrix.



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Monazite-(Ce) with Xenotime from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12083a.JPG] Monazite-(Ce) with Xenotime from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12083b.JPG] Monazite-(Ce) with Xenotime from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12083c.JPG] Monazite-(Ce) with Xenotime from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12083d.JPG]


No. MON 12083 - $ 250.00 SOLD

Monazite-(Ce) with Xenotime

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 5.3 x 4.2 x 2.5 cm (small cabinet)
Largest Monazite Crystal: 0.5 cm.


A nice full-size miniature specimen featuring a few scattered, pinkish-orange color heart-shaped twinned crystals of Monazite-(Ce) associated with a few small (1 mm + ), gemmy, prismatic, tetragonal crystals of Xenotime which exhibit a color change from pale greenish-yellow in incandescent lighting to a reddish-orange hue under spiral energy saver bulbs. This is the only piece that I can say for certain has Xenotime crystals on it, but other pieces in this update may have associated Xenotime as well.

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Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12084a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12084c.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12084b.JPG]


No. MON 12084 - $ 600.00

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 6.5 x 4.7 x 3.0 cm (small cabinet)
Largest crystal: 0.9 cm.


A nice display specimen with several orange-pink, sharp, lustrous, twins (plus some multiple twins) of Monazite-(Ce) perched upon gem quality, thin, prismatic Quartz crystals on matrix.

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Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12085a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12085b.JPG]


No. MON 12085 - $ 650.00

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 3.6 x 2.3 x 1.8 cm (miniature)
Largest crystal: 1.1 cm.


A remarkable piece for a smaller specimen. In all honesty, this piece should be trimmed down to a top notch thumbnail, because it would only accentuate the already large crystals on the specimen. There is a beautiful X-shaped twin on this piece (the best photo of it is pictured at the top of the page where I showed the color change photos) which is accompanied by a larger twinned crystal group. For the quality and beauty of the piece, it surely is one of the best pieces pound for pound in this update.

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Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12086a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12086b.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12086c.JPG]


No. MON 12086 - $ 300.00

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 3.5 x 2.8 x 2.4 cm (miniature)
Largest crystal: 0.6 cm.


An fine little toenail specimen with a good amount of translucent, lustrous, sharp, "X"-shaped, twinned, pinkish-orange crystals associated with water-clear thin crystals of Quartz on matrix.

To order this specimen click here




Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12087c.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12087a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12087b.JPG]


No. MON 12087 - $ 550.00 SOLD

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 4.1 x 4.0 x 2.2 cm (miniature)
Largest crystal: 0.9 cm.


This small miniature specimen hosts a few gorgeous twinned crystals of Monazite-(Ce) with excellent luster, translucency and sharpness sitting on glassy, transparent Quartz crystals on matrix. The main X-shaped twin on this piece is especially nice, and they are some of the largest crystals in the lot.

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Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12088b.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12088c.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12088a.JPG]


No. MON 12088 - SOLD

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 5.1 x 4.0 x 2.6 cm (small cabinet)
Largest crystal: 0.6 cm.


This piece is loaded with dozens of gorgeous butterfly wing-shaped or rabbit ears-shaped twinned crystals of Monazite-(Ce). The crystals on this specimen are very rich in color and have excellent sharpness, luster and translucency. The upper portion of the specimen features a few sharp, striated cubic crystals on Pyrite which along with the Monazite crystals are sitting atop slender, gem quality, colorless, hexagonal prisms of Quartz on porphyry matrix.

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Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12089a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon12089b.JPG]


No. MON 12089 - $ 275.00 SOLD

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 4.6 x 3.1 x 2.3 cm (miniature)
Largest crystal: 0.5 cm.


Several attractive, lustrous, sharp, butterfly and X-shaped twinned crystals of Monazite-(Ce) sit amongst water-clear, colorless Quartz crystals on this good-looking miniature size display specimen.

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Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120810a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120810b.JPG]


No. MON 120810 - SOLD

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 4.4 x 3.8 x 3.1 cm (miniature)
Largest crystal: 0.6 cm.


Here we have a good miniature specimen from this find. It hosts several fine, sharp, lustrous, translucent, pinkish-orange twinned crystals including a beautiful pair of butterfly twins as illustrated in the close up photo.



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Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120811a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120811b.JPG]


No. MON 120811 - $ 200.00

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 5.1 x 4.6 x 2.6 cm (small cabinet)
Largest crystal: 0.6 cm.


A very good representative specimen of this material featuring a few fantastic little X-shaped twinned crystals of a pinkish-orange color with good luster and sharpness. The piece was not the easiest to photograph, but certainly is a good buy for the quality and size of the crystals.

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Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120812a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120812b.JPG]


No. MON 120812 - $ 150.00

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 5.2 x 3.2 x 2.4 cm (small cabinet)
Largest crystal: 0.7 cm.


This specimen features a few isolated, sharp, lustrous, orange-pink color X-shaped twinned crystals of Monazite-(Ce) associated with thin, sharp, transparent colorless Quartz crystals on porphyry matrix.

To order this specimen click here




Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120813a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120813b.JPG]


No. MON 120813 - $ 425.00

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 6.4 x 5.3 x 2.7 cm (small cabinet)
Largest crystal: 0.9 cm.


This is certainly one of the best buys in the lot due to the fact that it features a very sculptural multi-twinned crystal of Monazite-(Ce) that measures nearly a full centimeter, which is huge for this locality. The piece could be trimmed down a bit to reduce the crystal to matrix ratio, but its still a very good specimen and would certainly make many collectors happy just the way it is.

To order this specimen click here




Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120815b.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120815a.JPG]


No. MON 120815 - $ 350.00

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 7.1 x 6.4 x 4.0 cm (small cabinet)
Largest crystal: 0.6 cm.


This small cabinet specimen hosts a handful of fine, sharp, lustrous, translucent, pinkish-orange twinned crystals sitting atop gem quality, needle like Quartz crystals. The fact that the Monazite crystals are fairly isolated is a nice tough, and you can clearly see the beautiful pair of butterfly twins illustrated in the close up photo.

To order this specimen click here




Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120816a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120816b.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120816c.JPG]


No. MON 120816 - $ 250.00

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 5.3 x 3.3 x 2.3 cm (small cabinet)
Largest crystal: 0.9 cm.


This is a wonderful large miniature specimen featuring a very eye-catching, isolated, multi-twinned crystal group of Monazite-(Ce) on Quartz crystals on matrix. This cluster of twinned crystals is one of the largest in the lot, and as you can see in the photos, its a really beautiful group that makes it one of the best smaller pieces in this lot.

To order this specimen click here




Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120817a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120817b.JPG]


No. MON 120817 - SOLD

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 5.0 x 3.3 x 2.5 cm (miniature)
Largest crystal: 0.6 cm.


This specimen hosts a single, light pinkish-orange color multi-twinned crystal cluster of Monazite-(Ce) in a nest of white, gemmy, prismatic Quartz crystal matrix. A perfect specimen for any collector who prefers to have isolated crystals on matrix. In my experience, it is very difficult to obtain specimens like this with one twinned crystal group on matrix.



To order this specimen click here




Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120818a.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120818b.JPG] Monazite-(Ce) from Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia [./MonBol1208/Mon120818c.JPG]


No. MON 120818 - SOLD

Monazite-(Ce)

Locality: Contacto vein, Siglo XX mine, Llallagua, Bustillo Province, Potos Department, Bolivia

Specimen Size: 6.7 x 3.7 x 2.9 cm (small cabinet)
Largest crystal: 0.7 cm.


This piece is loaded with several very good sized, blocky, sharp, pinkish-orange color, X-shaped, heart-shaped and butterfly twinned crystals on Monazite which are densely packed against a matrix of gemmy prismatic grey to colorless Quartz crystal matrix. This specimen displays beautifully and theres a lot of Monazite crystals on this one. For the size and aesthetic beauty, this is definitely one of the better specimens of this material that I have seen.



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