Mapping the world ... one micron at a time

Watch out for the August issue of Elements, the International Magazine of Mineralogy, Geochemistry, and Petrology. On page 228 you will find the first in a series of thematic advertisements of FEI's SEM-based Petrographic Analyzers. Elements publishes peer-reviewed papers which are part of a theme based collection. This issue is on "When the Continental Crust Melts", and FEI Natural Resources contributed with an amazing QEMSCAN® image of a garnet schist from Brittany, France.

The compositional map of the schist shows spectacular regional metamorphic textures. Schistocity is the term referring to a mode of foliation typical for medium-grade metamorphic rocks, where platy minerals such as micas and clays (in shades of green) are parallel aligned. Quartz (pink) occurs in form of elongated, drawn-out grains. The garnet group crystals (purple) are hexagonal in cross-section and really stand out in this piece of art. Garnets are important minerals in establishing the temperature-time histories of metamorphic rocks.

We would like to take this opportunity and thank Michael Garrick for providing the sample, a beach pebble he picked up as an undergraduate geology student. We used this sample to develop QEMSCAN® mineral identification protocols based on the latest generation of the Spectral Analysis Engine in iDiscover version 5.x.

QEMSCAN studies of metamorphic rock samples

Identification of key minerals is of great importance to determining the tectonic history of metamorphic samples. These key minerals may be few in number and present only as small micro-inclusions making them difficult to identify, if at all, with a petrographic microscope.


Once relict minerals of earlier metamorphic assemblages are located, thermobarometry and geochronology can then be applied, resulting in a wealth of information on previous segments of the pressure-temperature-time-deformation path. The relict mineral textures and their relationship to the fabric of the entire thin section can be easily seen in mineral maps yielding important textural information.


The QEMSCAN at the Camborne School of Mines (CSM) is being used to study metamorphic samples from the Central Metamorphic terrane of the Eastern Klamath Mountains, Northern California.


Intial results were presented at the European Geosciences Union, General Assembly, Vienna, 2-7 May 2010 "Application of Automated SEM-EDS Based Mineral Identification Systems to Problems in Metamorphic Petrology" by Robert Fairhurst, Wendy Barrow and Gavyn Rollinson.