XRF and EDXRF

X-ray fluorescence analysis (XRF) determines the chemical elements in a material. In gemmology the energy-dispersive variant, EDXRF for short, is most commonly used.

The principle

The stone is excited with X-rays. The atoms in the material then emit their own secondary X-rays, whose energy is typical of each element. A detector measures these energies and their frequency. This shows which elements are present and in approximately what amounts.

What EDXRF is used for

• Identification: major elements show whether a material fits the expected species
• Cause of colour: chromium, iron, vanadium, copper or manganese can be detected, for example the copper in Paraíba tourmaline
• Origin: ratios of trace elements such as gallium, iron or vanadium in corundum, together with inclusions, offer clues to the deposit
• Treatment and synthesis: unusual elements can point to flux, lead-glass fillings or coatings

The limits

EDXRF measures close to the surface. Coatings or residues can affect the result. The geometry of the stone, its size and its orientation to the detector influence the readings. Light elements such as beryllium or lithium cannot be detected, and for very low trace concentrations the method is often not sensitive enough. For these, laboratories use LA-ICP-MS.

Non-destructive and fast

A major advantage is that the stone remains intact and the measurement takes only a few minutes. EDXRF is therefore suitable as an overview analysis before more elaborate methods are used.

Working together

Origin determination never rests on a single measurement. A laboratory combines chemistry, spectroscopy and inclusions and compares them with reference stones of known origin.

In brief

EDXRF shows quickly and non-destructively which elements a stone contains. It helps with identification, cause of colour, treatment and origin. It does not capture light elements or very low concentrations; LA-ICP-MS is available for these.

At NOBILITH

Origin statements in the dossier come from the laboratory's report. The Academy explains the methods behind them so that it is clear what such a statement rests on and where its limits lie.

Sources

• GIA: Gems & Gemology, articles on EDXRF and origin determination
• SSEF: explanatory notes on analytical methods