Matura diamond is a historical and commercially deprecated trade name for colourless or near-colourless zircon recovered from the Matara (older spelling Matura) district on the southern coast of Sri Lanka. The name is a misnomer in the modern sense — the material is not diamond but the silicate mineral zircon, ZrSiO4 — and the term survives chiefly in older trade literature, antique-jewellery descriptions, and gemmology coursework as a cautionary example of nineteenth-century commercial naming.

The material

Zircon is a tetragonal silicate of zirconium and one of the older silicate minerals known to the trade, with significant deposits in Sri Lanka, Cambodia, Myanmar, Thailand, Tanzania and Australia. It occurs across a wide colour range — colourless, yellow, brown, red, green, and the heat-treated blue characteristic of most modern jewellery zircon. Sri Lankan material from the Matara alluvials is historically the source of the colourless variety that gave rise to the Matura name.

Colourless zircon has gemmological properties that, by the standards of the eighteenth and nineteenth centuries, made it a credible visual stand-in for diamond when set in closed-back mounts. Its refractive index of approximately 1.92 to 1.98 and dispersion of 0.039 are higher than those of most other colourless gem materials apart from diamond itself, producing a strong brilliance and noticeable fire. Hardness, however, is markedly lower at 6 to 7.5 on the Mohs scale, and zircon is brittle and prone to facet-edge abrasion, particularly on stones of the high (low-density) variety.

The trade name

The trade adopted the term Matura diamond in the eighteenth and nineteenth centuries when colourless zircon from the Matara district was traded into European markets. The name was used both descriptively — to indicate origin — and aspirationally, to associate the material with diamond. It is now classified as a misleading varietal name under the trade-naming guidance issued by the World Jewellery Confederation and most gemmological laboratories, which prohibit the use of diamond as a qualifier for any non-diamond species.

Equivalent misleading names from the same period include Ceylon diamond, Matara diamond and Hyacinth diamond, all of which referred to zircon and all of which are now considered improper. Modern terminology requires the simple species name zircon, with origin given separately.

Identification

Zircon is readily distinguished from diamond by a competent gemmologist on the basis of refractive index (1.92–1.98 versus 2.42), specific gravity (typically 4.6–4.7 for high zircon versus 3.52 for diamond), strong birefringence visible as facet doubling under magnification, and characteristic absorption lines in the visible spectrum. Heat-altered or low-type zircon shows a distinctive set of broad bands rather than the sharp lines of unaltered material. None of these features is shared with diamond, and confusion in the modern laboratory is impossible.

Status today

Specimens described as Matura diamonds in nineteenth-century settings are encountered in the antique and estate trade, particularly in Georgian and Victorian work where the closed-back mount and silver-on-gold construction produced sufficient face-up brightness for the deception to function. Such pieces have value as period work and as examples of gemmological history, and their material is properly described in any modern report or catalogue as colourless zircon, with the historical trade name noted only for context.