Reply When writing that some petrologists have chosen to get around the problem caused by oxidation of Fe-Ti-oxides during the initial cooling of basalts by using an arbitrary value of the Fe203/FeO ratio instead of the one given by the analysis, it was not my intention to disparage the aims of petrologists concerned with genetic problems - rather to make a suggestion I hope will be helpful....

Orthoomphiboles wiih pronounced iridescence are found i n eight localities i n the vicinity of Nuuk, the capital of Greenland. The iridescence, difficult to see on rough samples, becomes clearly visible when the material is cut. This iridescent orthoamphibole is mined by a company wholly owned by Nuuk commune, and is sold under the trade name Nuummite. This orthoamphibole has a composition similar to that of iridescent orthoamphiboles described earlier from Greenl~nd as well as from New Hampshire and Massachusetts, but is believed to be the first such orthoamphibole to be regarded as a gemstone. LOCATION AND OCCURRENCE To date, the iridescent orthoamphiboles have been found in eight localities within 50 lzm (approximately 30 mi.) of Nuulz, the capital of Greenland.

T h e red variety of the mineral tugtupite, a rare silicate closely related to sodalite, has been used as a gemstone since 1965. This article presents the history of the mineral and details of its mineralogy and gemology. A recently discovered light blue variety of tugtupite is also described. Thus far, tugiupite has been found in only t w o localities: (1) Lovozero, Kola Peninsula, U.S.S.R., where it occurs as very small1 grains; and (2) Ilimaussaq, South Greenland, where it has been located at several places within the Ilimaussaq intrusion. Gem-quality tugtupite has come almost exclusively from one occurrence, a set of hydrothermal albite veins from the Kvanefjeld plateau i n the northwestern corner of the Ilimaussaq intrusion.

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