Distinguishing Rare Earth Minerals with a Field Portable Spectrometer

Rare earth elements (REEs) have recently become critical worldwide for use in modern technology. We use rare earth elements in several commercial applications as components in smartphones, digital cameras, LED lights, and flat-screen TVs. For example, dysprosium is used for permanent magnets, europium for phosphors and fuel cells, terbium for phosphors and permanent magnets, and yttrium for red phosphor, fluorescent lamps, ceramics, and metal alloys. We also use REEs for clean energy and defense technologies.

REEs include:

  • Europium
  • Gadolinium
  • Terbium
  • Dysprosium
  • Holmium
  • Erbium
  • Thulium
  • Ytterbium
  • Lutetium
  • Yttrium
  • Lanthanum                 
  • Cerium
  • Praseodymium
  • Neodymium
  • Samarium

Due to the high demand for REEs, exploration efforts have increased tremendously. One can find most rare earths in uncommon types of igneous rocks, especially alkaline rocks and carbonatites. Minerals such as euxenite, bastnaesite, xenotime, monazite, and allanite are indicative of REEs. Distinguishing between the different rare earth minerals is crucial in the exploration phase.

Portable field spectrometers, like Spectral Evolution's oreX- Series, are well suited for exploration geologists looking for all types of REE deposits. While rare earth elements all show absorption features in the 350nm-2100nm region, geologists can distinguish between them by looking at the differences in their specific spectral features. Below is a comparison between Monazite, Xenotime, and Bastnaesite.


All three of the rare earth minerals shown have unique spectral features. Bastnaesite, a rare earth mineral in the carbonate group, has numerous sharp absorptions (f-f orbital electronic transitions) throughout the 0.35 to 2.5-micron region, which we assume is due to variable proportions of lanthanide series rare earth elements (i.e., Nd, Sm, and others). In the SWIR, we see overlapping absorptions, broader bands, and vibrational absorptions due to CO3 combination. Overtone bands are not present in Monazite or Xenotime because they are part of the Phosphate group. Xenotime has several sharp spectral absorptions (f-f orbital electronic transitions) throughout the 0.35 to 1.8-micron range. This is due to variable proportions of heavy lanthanide series rare earth elements (i.e., Dy, Er, Ho, and Yb). Monazite has absorptions at 550nm, 680nm, 750nm, 810nm, and 880nm, which all stem from electronic transitions in the Nd3+ and Sm3+ ions.