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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