HORIBA Raman instruments — principally the LabRAM and XploRA series manufactured by HORIBA Scientific — represent a class of confocal Raman microspectrometers widely adopted by advanced gemmological laboratories, university mineralogy departments, and major gem-testing institutes. By directing a monochromatic laser onto a sample and analysing the inelastically scattered photons that result, these systems generate a molecular fingerprint that can identify a gemstone species, detect structural modifications introduced by heat or irradiation treatment, and characterise microscopic inclusions — all without removing material from the stone.

Operating Principle

Raman spectroscopy exploits the Raman effect: when laser light interacts with a material, a small fraction of photons exchange energy with molecular vibrations, shifting to higher or lower frequencies. The resulting spectrum — a plot of scattered intensity against wavenumber shift (cm⁻¹) — is effectively unique to a given mineral phase. HORIBA's confocal optical design allows the laser focus to be placed at a precise depth within a transparent gem, enabling analysis of individual inclusions or growth zones without interference from surface coatings or surrounding host material.

The LabRAM series is a fully integrated confocal Raman microscope platform offering interchangeable laser wavelengths (commonly 473 nm, 532 nm, 633 nm, and 785 nm), high-dispersion gratings, and motorised mapping stages. The XploRA series is a more compact, application-focused variant designed for routine laboratory throughput while retaining research-grade spectral resolution. Both platforms interface with HORIBA's LabSpec software suite, which includes spectral databases and automated fitting routines.

Gemmological Applications

In a gemmological context, HORIBA Raman systems are employed for several categories of analysis:

• Species and variety identification: Distinguishing corundum from spinel, alexandrite from synthetic alexandrite, or jadeite from nephrite on the basis of characteristic Raman peaks rather than refractive index or density alone.
• Treatment detection: Identifying filler materials in fracture-filled rubies and emeralds (glass, resin, or oil each produce distinct Raman signatures), detecting beryllium-diffusion effects in corundum through associated mineral phases, and recognising polymer coatings on turquoise or lapis lazuli.
• Inclusion characterisation: Determining the mineral identity of solid inclusions — for example, confirming a rutile silk in sapphire, identifying a pyrite crystal in lapis lazuli, or distinguishing a protogenetic mineral in an emerald to support origin determination.
• Synthetic and simulant separation: Differentiating natural diamond from moissanite, CVD diamond from HPHT diamond, and natural coloured stones from their hydrothermal or flux-grown counterparts.

Use in Major Laboratories

Institutions including the Gemmological Institute of America (GIA), the Swiss Gemmological Institute (SSEF), Gübelin Gem Lab, and Lotus Gemology have incorporated confocal Raman microspectrometry — including HORIBA platforms — into their analytical workflows. The technique is particularly valued for its non-destructiveness and its ability to resolve ambiguous cases that cannot be settled by conventional refractometry, spectrophotometry, or standard fluorescence testing. Raman mapping, in which spectra are collected across a two-dimensional grid, allows spatial distribution of phases to be visualised — a capability relevant to the study of composite stones and heavily included specimens.

Limitations and Context

HORIBA Raman instruments are capital-intensive and require trained operators capable of interpreting spectra and managing fluorescence interference, which can obscure Raman signals in heavily included or dyed stones. They are therefore instruments of the research and high-end commercial laboratory rather than the retail trade counter. Complementary techniques — infrared spectroscopy (FTIR), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and UV-Vis-NIR spectrophotometry — are routinely used alongside Raman analysis to build a complete analytical picture, particularly for origin determination reports.