By The tourmaline species with the ornamental application can be separately described. Though elbaite, liddicoatite, uvite and dravite provide the majority of gemstones, brief notes on the other species can be given. Buergerite is found as transparent to translucent crystals, dark brown to yellow and would be sought as a mineral specimen. Good examples have been found in the Mexquitic area, San Luis Potosi, Mexico.
Chromdravite occurs as small acicular dark green gemstones crystals and has been found in Kareliya, Russia. Feruvite occurs only as grains. Foitite forms bluish black crystals which may reach 20 mm; one location is a pegmatite at the white Queen mine, Pala, California, USA. Magnesiofoitite crystals found in Yamanashi Prefecture, Japan, have not yet been described.
Olenite forms on the outer rim of acicular crystals with elbaite cores and has been found in the Kola Peninsula, Russia. Povondraite (originally defined as ferridravite) forms very small black crystals at a deposit in Bolivia. Rossmanite has been found in granite pegmatites as colourless to pale pink crystals; locations have been identified in Canada. The black tourmaline group mineral schorl occurs as long to short prismatic crystals and occurs in granite pegmatites and elsewhere. Vanadiumdravite forms very small dark green to yellow crystals at locations in the lake Baikal
area of Russia.
From the point of view of the gemmologist it is not necessary to differentiate between the different tourmaline species – the existence of solid solution series between some tourmaline group members (between elbaite and dravite, for example) complicates differentiation Colour zoning giving the familiar watermelon appearance with the redcore and green rind is a feature of elbaite, the cause arising from more than one event, including a change of composition during growth. In the ordinary ray the pleochroic colours range from pink to pale green, pale to deep blue; in the extraordinary ray the crystals may show colourless to yellow, olive blue or purplish.
