Prase — Leek-Green Chalcedony from the Collector's Drawer
Prase — Leek-Green Chalcedony from the Collector's Drawer
A muted green chalcedony coloured by actinolite or chlorite inclusions, less commercial than chrysoprase but historically significant
Prase is a translucent leek-green variety of chalcedony coloured by microscopic inclusions of actinolite or chlorite. The name derives from the Greek prasinos, meaning leek-green, and was historically applied across European mineralogy to a range of dull green silicates before being narrowed to the chalcedony variety in nineteenth-century classifications. Prase is distinct from chrysoprase (chalcedony coloured by nickel) and from green agate (banded green chalcedony of varied colourants), and although the term is no longer widely used in commercial trade, it remains in the gemmological vocabulary for a specific inclusion-coloured material with its own classical history.
Composition
Prase is fundamentally cryptocrystalline silica, SiO2, with the colour derived not from a chromophore in solid solution but from suspended fibres or platelets of green amphibole or chlorite. The inclusion phase determines the precise hue and saturation: actinolite-included prase tends toward bright leek-green, while chlorite produces a more muted, slightly bluish or olive cast. Translucency depends on inclusion density and grain size, ranging from near-opaque dark green to translucent grass-green in the better material.
Physical properties match other chalcedonies: hardness 6.5 to 7 on the Mohs scale, specific gravity around 2.58 to 2.64, and refractive index near 1.53 to 1.54. Lustre is waxy to vitreous on polished surfaces.
Sources
Historic European production came from Salzburg in Austria, the Erzgebirge of Saxony in Germany, Breitenbrunn, and various Scottish localities. These sources supplied the bulk of nineteenth-century cabinet stones and the seal stones and beads that appear in Victorian and Georgian European jewellery. Modern production is occasional rather than systematic, with reports of prase from Madagascar, India, and the western United States, but the term is rarely used in current commercial catalogues — the same material is more often sold as green chalcedony or actinolite-included quartz.
In the trade
Prase is fashioned as cabochons, beads, seals, and intaglios. Its muted colour and waxy translucency suit it to classical seal-stone work and to revivalist Victorian-style jewellery, and it appears in antique brooches, watch fobs, and signet pieces. Modern faceted prase is rare; the inclusions that produce the colour also limit clarity, and the material reads better in cabochon than in faceted cuts.
Pricing reflects the limited demand. Prase trades at a fraction of chrysoprase pricing for comparable colour saturation, partly because chrysoprase's apple-green is more commercially desirable and partly because chrysoprase commands a recognised name premium. For collectors of inclusion-coloured silica and for jewellers working in period-revival idioms, prase is an affordable and historically appropriate choice.
Identification
Magnification is the diagnostic key. The dark green needles or platelets visible in transmitted light, especially under fibre-optic illumination, distinguish prase from chrysoprase (which shows no comparable inclusions and whose colour is uniformly distributed) and from heat-treated dyed quartz simulants. Refractive index, specific gravity, and Raman or FTIR identification of the included phase can confirm the species in laboratory work.
Care
Prase shares the care profile of other chalcedonies. Mild soap, warm water, and soft cloth cleaning are appropriate; ultrasonic and steam cleaning are generally safe but should be avoided on stones with visible cracks or stress fractures. The material is durable enough for ring use in protected settings.