Hydrogen-rich diamond is a diamond whose infrared absorption spectrum shows unusually strong hydrogen-related features, typically a sharp band at 3107 cm with associated peaks at 1405, 4495 and 7355 cm. Hydrogen is incorporated as a trace impurity in the diamond lattice, often in association with nitrogen and vacancies, and at high concentrations it produces distinctive optical and visual effects. Hydrogen-rich diamonds appear in a range of colours including grey, brown, violet, chameleon and certain greens.

Geological context

Hydrogen-rich diamonds are generally Type Ia, with aggregated nitrogen, and are most often associated with mantle environments where hydrogen-bearing fluids participated in diamond growth. Notable production has come from Argyle in Western Australia, Marange in Zimbabwe, the Premier (now Cullinan) mine in South Africa, and certain alluvial sources in West Africa. The Argyle pinks famously included a small parallel population of hydrogen-rich grey-violet stones; the Zimbabwean Marange field produces large volumes of hydrogen-rich brown and grey-green material at lower per-carat values.

Optical effects

The hydrogen system contributes to several visually striking phenomena:

• Chameleon diamonds, which change colour reversibly between greenish-yellow and a more saturated yellow on gentle heating or after prolonged storage in darkness, owe their colour change in part to hydrogen-related defects.
• Violet to grey-violet diamonds, particularly those from Argyle, derive their hue from hydrogen-related absorption bands centred near 550 nm.
• Some grey, brown and olive diamonds with high hydrogen content show pronounced cloud-like internal graining and a milky or hazy appearance.

Identification

Hydrogen-rich character is established by FTIR spectroscopy. The 3107 cm peak is the canonical marker; its strength relative to the diamond's two-phonon absorption gives a quantitative measure of hydrogen incorporation. UV-visible spectra and photoluminescence add detail, particularly for chameleon and violet stones where multiple hydrogen-related centres operate together.

Hydrogen-rich diamonds are virtually always natural; HPHT and CVD synthetic processes do not generally produce comparable hydrogen-related signatures, although CVD growth can incorporate hydrogen in different defect configurations that the laboratories distinguish. The practical implication is that strong 3107 cm absorption is a reliable indicator of natural origin, useful as a screening flag in mixed parcels.

Trade considerations

Hydrogen-rich diamonds occupy specialist niches in the coloured-diamond market. Argyle violets and chameleon diamonds command significant premiums when colour and clarity are favourable, with auction records well into six figures per carat. Marange-type hydrogen-rich brown and grey material trades at comparatively modest prices and supplies industrial as well as jewellery channels. As with all fancy-coloured diamonds, a current report from a recognised laboratory is essential, and the relevant treatment-disclosure protocols should be followed.