One of Raman's best known applications is the identification of mineralogical phases. Raman spectroscopy is a NON-DESTRUCTIVE technique, which is an important factor, because it does not compromise the appearance of the sample and does not affect the possibility of further analysis.
We are a team of graduates in Earth Sciences, chemical experts and mineral collectors with different experiences and ages: some of us are already "Ramanists" and we are all collectors of minerals with a focus on micro collection; our head office is in Padua.
We have always felt the need to answer the questions associated with the interpretation of labels on our samples and now we are able to make a leap forward in the identification of mineralogical species. We are happy to share this experience with mineralogy enthusiasts.
The mineralogical samples sent by collectors (Important technical informations) are analysed using a micro-Raman-dedicated spectrometer (Working Tools) which returns a spectrum (Some theory) containing useful information for the identification of the mineral phase. This phase is identified by comparing the spectrum of the sample analysed with a reference spectrum and, if necessary, with the information provided by scientific literature. The result of the spectrum analysis is sent to the collector as a digital report (Example), containing:
As we know, a mineralogical species is identified by the combination of different analytical techniques, but, in many cases, Raman micro-spectroscopy is already sufficient.
Our Raman micro-spectroscopy equipment meets the requirements of today's highest quality standards. We have a Raman XploRA™ PLUS (HORIBA Scientific) confocal microscope, equipped with a green laser (wavelength of 532 nm, which is more versatile for mineralogical samples) and with Olympus 10X, 50X long working distance and 100X lenses, which allows us to obtain a high spatial resolution (<1 μm).
This tool has a motorized goniometric cradle along the X-Y-Z axes with micrometric movement that can be operated remotely. The image is captured by the 3.1 mp CMOS camera directly connected to the computer 23" monitor. The Raman spectrum is acquired by a CCD detector and the spectral resolution can be modified thanks to the presence of four monochromators (diffraction gratings of 600 gr/mm, 1200 gr/mm, 1800 gr/mm, 2400 gr/mm). The acquisition and processing of the Raman spectrum is managed via LabSpec 6 software. Identification of the mineralogical phases is done using CrystalSleuth software (Laetsch et Downs, 2006) and, in some cases, using the information provided by scientific literature.
Laetsch T., Downs R. (2006) Software for identification and refinement of cell parameters from powder diffraction data of minerals using the RRUFF Project and American Mineralogist Crystal Structure Databases. Abstracts from the 19th General Meeting of the International Mineralogical Association, Kobe, Japan, 23-28 July 2006
Raman spectroscopy is a technique for the analysis of materials based on the Raman effect (or Raman scattering), described by Indian physicist Chandrasekhara Venkata Raman (1888 - 1970), awarded the 1930 Nobel Prize for Physics. The Raman effect is the inelastic scattering of a photon hitting an object (incident radiation) and is caused by the interaction between the photons and the molecular vibrations of the object. In other words, when an object is hit by a beam of light, in addition to scattering the light radiation with the same wavelength of the incident wave (elastic scattering), it also diffuses the light with wavelengths shorter or longer than the original one, because of the exchange of energy between the photons and the molecule involved (the Raman effect).
According to the principle of Raman spectroscopy, a monochromatic light beam (usually a laser) hits the object to be analysed and the scattered radiation is decomposed in its wavelengths by a monochromator. The result of this decomposition is a Raman spectrum (which usually provides the values of the difference in the number of waves expressed in cm-1, between the observed radiation and the incident radiation) which contains information on the chemical composition and the molecular structure of the analysed substance.
In mineralogy, Raman spectra are used to identify the mineral (qualitative analysis) compared to the reference spectra reported in the literature.
A Raman spectrometer consists of:
Samples to be analysed must be accompanied by an authorisation/shipping form (link to the section) by which the collector specifies the number of samples, their origin and provides a brief description of the minerals to be analysed. Samples must meet the following requirements:
In many cases, Raman micro-spectroscopy analysis is sufficient to identify the mineral phase with a reasonable degree of certainty; if you want to increase the degree of certainty, further analysis with other techniques (such as SEM-EDS, FT-IR, X-ray diffractometry, etc.) is necessary because only the combination of multiple analytical methods leads to highly reliable results.
In any case, the Raman micro-spectroscopy analysis is very useful because: