Native Element — Single-Element Minerals in Gemmology
Native Element — Single-Element Minerals in Gemmology
Diamond, gold, silver, copper, sulphur — the minerals composed of one element in uncombined form
A native element is a mineral composed of a single chemical element in uncombined elemental form. The category sits at the head of the Dana mineral-classification system as Class I and at the head of the Strunz classification as Class 1, reflecting its historical position as the most chemically simple group of minerals. In gemmology, the native elements that matter are diamond (carbon), gold, silver, copper, and platinum, with smaller and more specialised relevance for graphite, sulphur, arsenic, antimony, bismuth, and a handful of platinum-group elements that occur in their elemental form in primary and placer deposits.
Sub-classification
Native elements are conventionally divided into three groups by chemical character. The metals — gold, silver, copper, platinum, palladium, iridium, osmium, ruthenium, and rhodium — share metallic bonding, high density, ductility, and metallic lustre. The semi-metals — arsenic, antimony, bismuth — show partial metallic and partial covalent character, with brittleness and lower conductivity. The non-metals — diamond, graphite, sulphur, selenium, tellurium — are covalently or molecularly bonded with very different physical properties, of which only diamond and to a much lesser extent sulphur have gem-trade significance.
Within the metals, the platinum group (Pt, Pd, Ir, Os, Ru, Rh) and the gold-silver-copper group are the two principal sub-clusters. The platinum group elements often occur together in solid solution, as in iridosmine and osmiridium; the gold-silver group also forms solid solutions, with electrum being a natural gold-silver alloy.
Diamond as a native element
Diamond is the dominant native-element gem material. It is pure carbon in cubic crystal form, hardness 10 on the Mohs scale, refractive index 2.417, dispersion 0.044. The other naturally occurring polymorphs of carbon — graphite (hexagonal) and lonsdaleite (also hexagonal, found principally in meteorites) — are not gem materials. Diamond's geological setting is extreme: most gem-quality diamonds form in the Earth's mantle at depths of 150 to 250 kilometres under temperatures and pressures sufficient to stabilise the carbon-cubic phase, and are brought to the surface by kimberlite and lamproite eruptions. A small but important sub-population of diamonds — the Type IIb blues, the deep-source pink-purple stones, and certain large white stones — formed at greater depths still, in the lower mantle.
Gold
Native gold is the second-most-significant native element in gem and jewellery contexts. Gold occurs in primary hydrothermal vein deposits, where it is associated with quartz, pyrite, arsenopyrite, and other sulphides, and in placer deposits, where it has been concentrated by stream action from weathered primary sources. Native gold is rarely pure: most natural gold contains 5 to 25 per cent silver in solid solution, with smaller amounts of copper, palladium, and other metals. Electrum, a gold-silver alloy with silver content above approximately 20 per cent, is a recognised mineral name with classical antiquity.
Native gold is occasionally used directly in jewellery as natural nuggets, particularly from Alaskan, Australian, and Californian sources, though most gold for jewellery is refined to standard alloys before fabrication. The historical mineralogical literature documents large nuggets — the Welcome Stranger nugget from Victoria, Australia (78 kilograms), the Hand of Faith nugget (27 kilograms) — that are themselves objects of value beyond their bullion content.
Silver, copper, and the platinum group
Native silver is less common as direct gem material but occurs in spectacular crystal specimens, particularly from the historic mining districts of Kongsberg (Norway), Cobalt (Ontario), and Freiberg (Saxony). Native copper is most often encountered as the famous wire and dendritic specimens from the Keweenaw Peninsula of Michigan and from Cornwall. Both are mineral-collector specimens rather than mainstream jewellery materials. Native platinum and the platinum-group elements occur principally in placer deposits and in primary chromite-rich igneous bodies; the historic source is the Urals, with modern production from South Africa and Russia.
Sulphur and other non-metals
Native sulphur, with its distinctive yellow colour and crystal habit, is a mineral-collector specimen and occasionally a curio cabochon or carving. The volcanic fumarole sulphur of Sicily and Italy is the classical source. Graphite, the other major native carbon polymorph, is industrial rather than gem material. Bismuth, with its distinctive iridescent stepped crystals, is most often encountered in its synthetic crystallised form sold as a curio or specimen rather than naturally.
Identification
Identification of native elements relies on the standard suite of gemmological and mineralogical tools. For diamond, refractive index measurement (well above the limit of standard refractometers, requiring reflectance methods), thermal conductivity, and infrared spectroscopy distinguish it from synthetic moissanite, cubic zirconia, and other simulants. For native gold and silver, density and chemical analysis (X-ray fluorescence) confirm composition; the ductility and the absence of cleavage further differentiate native metals from sulphide minerals that share metallic lustre. The Dana and Strunz systems provide systematic identification keys; the standard mineralogy reference is Hurlbut and Klein's Manual of Mineralogy.