About Morganite: Gemstone Information
The colour is due to manganese. Caesium and rubidium often occur as impurities and may raise the SG and RI. Most pink beryls have an SG from 2.80 to 2.90 although some may be as low as 2.71. The RI is in the range between 1.578 and 1.600 for the ordinary ray and between 1.572 and 1.592 for the extraordinary ray, the DR varying between 0.008 and 0.009. Dichroism is distinct with a pale pink and a deeper bluish pink, the stronger colour in the extraordinary ray. There is no characteristic absorption spectrum and the luminescence under ultra-violet light is a weak lilac, but under X-rays there is an intense, but not bright, crimson glow. The pegmatites of Pala, southern California, have produced very fine morganites which can be polished into large gemstones. Crystals from the pegmatites of Madagascar have also produced gemstones.
Red beryl, transparent and of gem quality is coloured by manganese; small tabular crystals were first found in a rhyolite at a site in the Thomas Range of mountains in Utah, USA. Larger crystals were later fzound in the Wah Wah mountains in the same state.
The Wah Wah crystals, occurring in a white volcanic rhyolite, were longer, elongated rather than tabular and more transparent. Crystals are prismatic showing the first-order prism and a base. The colour has been described as raspberryred. In 1968 Nassau and Wood described the red beryl in American Mineralogist, 53, 801–806, manganese being cited as the cause of the colour. No water was found to be present and small clear areas occurred in some crystals. Faceted stones are very beautiful; in Standard Catalog of Gem Values, second edition, 1994, Miller and Sinkankas suggested that up to $100 a carat might be asked for crystals of the finest quality up to 4 ct. For faceted material up to 2 ct, up to $5000 a ct might be asked. Yellow beryls are obtained from practically all the localities mentioned for aquamarine. Particular localities are Madagascar, Brazil and Namibia. In Namibia, heliodor is found in association with aquamarine and a yellowish green variety at Klein Spitzkopie near Rossing on the Otavi railway east of Swakopmund, and also between Aiais and Gaibes on the Fish river. Some yellow beryls have been reported to show radioactivity due to their containing a trace of uranium oxide. A deep yellowish red variety of beryl, called ‘berilo bocade fogo’ (fire-mouth beryl), comes from Santa Maria do Suassui in Minas Gerais. Many localities in the USA produce yellow beryl but the only one of importance is the Merryall or Roebling mine at New Milford, Connecticut.
The new beryl-group mineral pezzottaïte is described in a major paper by Hawthorne et al. in The Mineralogical Record, 35, 369–378, 2004. The mineral is found in the Sakavalana pegmatite, Fianarantsola province, Madagascar. Rhombohedral crystals occur in three different habits; flat masses filling cavities between ‘cleavelandite’, quartz and tourmaline; subhedral to euhedral hexagonal tabular crystals up to 10 cm in diameter; and as small, flat to equant to elongated crystals attached to the faces of large tourmaline crystals. The colour is moderate red to pink with dichroic colours pink to orange and purplish pink to pinkish purple for the ordinary and extraordinary rays respectively. The RI for the same two rays is 1.612–1.620 and 1.601–1.611. No reaction to UV radiation has been reported. Crystals are brittle and show an imperfect cleavage in one direction. Pezzottaïte differs from other minerals of the beryl group by its essential Cs content and a superstructure arising from the ordering of Be and Li in tetrahedral coordination. Some chatoyant specimens and faceted stones are depicted in the Record paper