Raman Spectroscopy in Geology
Raman spectroscopy is a powerful analytical tool in geology and mineralogy, with advantages over alternative techniques.
- Little or no sample preparation
- Microscopic technique complements traditional petrographic analysis
- Unambiguous mineral discrimination
- Variety of sample types
- Combine with microthermometric techniques, SEM, high pressure and temperature cells
What can Raman Tell You?
- Composition of the material, from characteristic Raman frequencies – e.g. identify minerals, differentiate polymorphs
- Stress/strain state, from changes in frequency of Raman peak – e.g. crystal structure analysis, high pressure mineral studies
- Quality of the crystal, from the width of the Raman peak – e.g. crystallinity/amorphicity
- Crystal symmetry and orientation, from the polarisation of the Raman peak – e.g. orientation of crystals, band assignments
Advantages of Raman in Geology
- Analyse geological sample types:
- Standard petrographic thin sections (ideally without coverslips)
- Polished blocks
- Small hand specimens
- No sample preparation or damage
- This means you can go on to analyse your sample with other techniques such as SEM or EMPA.
- Study the crystallographic structure and subtle changes in chemistry
- Powerful identification
- Extensive libraries of comparison spectra
- Published spectra and online databases
- Unambiguous, unlike alternative techniques such as optical microscopy
- Fast analysis, usually less than 1 minute
Each mineral has a characteristic Raman spectrum, like a fingerprint. This is distinguished by the crystallographic structure, the masses of the atoms and the bond angles and lengths. This spectrum is a powerful discrimination tool, without the ambiguity of other techniques. Extensive databases are available to help you identify minerals, and you can also add your own spectra from well characterised samples.
Raman spectroscopy is also useful in gemmological laboratories, because of its non-destructive and unambiguous nature.
Families of minerals often have ‘marker’ bands. For example, carbonates have a strong, sharp band around 1085 cm-1.
Geological Sample Types
- Hand specimens
- Under upright microscope
- Free space microscope
- Flexible sampling arm
- Fibre optic probe
- Petrographic thin sections (standard 30 µm thick)
- Polished blocks, for economic ore mineralogy
- Doubly polished wafers, for fluid inclusion analysis
- Powder diffraction
- Single grains/crystals
Combining SEM and Raman (SEM-SCA)
Raman can be integrated with SEM (Scanning Electron Microscopy) for SEM-SCA (structural and chemical analysis), which has applications in geology and mineralogy. For example, you can then study opaque minerals and petrographic thin sections that do not transmit light. Other applications include:
- Alluvial deposits
- Heavy mineral sand refining
- Cement clinker
- Secondary electron imaging (SEI)
- Study sample morphology
- Backscattered electron imaging (BEI)
- Compositional and topographical contrast
- White light imaging
- Optical contrast (colour, reflectivity)
- Cathodoluminescence “flood” imaging
- Structural and chemical contrast
- X-ray mapping
- Spatial distribution of elements
- X-ray analysis
- Elemental composition
- Fast but insensitive to light elements
- Raman spectroscopy
- Chemical analysis
- Crystallinity, orientation and strain
- Very sensitive to changes in chemistry
- Photoluminescence (PL) spectroscopy
- Electronic information
- Cathodoluminescence (CL) spectroscopy
- Chemical information
Advantages of SEM-SCA in Geoscience
With Raman you can distinguish between polymorphs (e.g. TiO2, Al2SiO5), which is not possible with EDS.
The spatial resolution is better than optical petrography, due to the laser and SEM spot size.
Raman analysis can be performed in situ, maintaining the spatial context.
EDS analysis complements Raman spectroscopy by revealing subtle variations in concentration and the presence of trace elements
Standard thin sections can be viewed without additional preparation. This means you can then re-use them as you need to and also analyse them further with optical petrography.
Economic and opaque minerals can be fully characterised both quickly and easily.
The Renishaw InVia is a research-grade confocal Raman microscope, ideal for geological research.
- Powerful, reliable and easy to use
- Automate common tasks to save time
- Flexible accessories for specific applications
- Combine with SEM from all major manufacturers
Blue Scientific is the official Nordic distributor for Renishaw Raman systems. For quotes or further information about using Raman for specific geological applications, please get in touch: