Iowaite has been re-examined using new, well crystallized material from the Palabora open pit mine, Transvaal. Microprobe, carbon analyser and thermal analyses, powder and single-crystal X-ray diffraction, infrared, UV-visible and mass spectroscopic and optical studies were made. The ideal formula is Mg6Fe~II(OH)16C12.4HzO. It is trigonal, R3m, a = 3.1183(9), c = 24.113(8) A, V = 203.1(2).~3, Z = 3/8; Dobs 2.09 g/cm3; D~c 2.04 g/cm3; hardness (Mohs)=21. The interlayer C1-ions are displaced from the threefold axis. It is uniaxial negative, with ~ = 1.561 _ 0.002, ~ = 1.543 __+ 0.002; coloured crystals are intensely pleochroic, due to intervalence charge transfer between the Fe 3 + and Fe z+ substituting for Mg z+, with O pale yellow, E deep blue-green.

SUMMARY. m plot of seventy-five new analyses of members of the helvine group and fifty-seven analyses from the literature indicates complete miscibility between the Fe and Zn members (danalite and helvine) and between the Fe and Mn members (danalite and genthelvite). The new analyses include essentially pure helvine and genthelvite (for both of which X-ray data are presented) and the nearest approach to pure danalite (86 at. % Fe). Two new localities for genthelvite, the rarest member, are reported.IN the helvine group, R4Bea(SiO4)3S (R = Mn, Fe 2+, Zn), the member with Mn preponderant, helvine, is commoner than the Fe 2+ member, danalite, and the Zn member, genthelvite, is by far the rarest; only twelve analyses of genthelvite were found in the literature (six being incomplete analyses), and the largest and finest crystals described had not been analysed.

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ABSTRACT. Pitticite is re-examined analytically and found to be a gel-like mineral of widely varying composition. Previously reported minor amounts of accessory elements are indeed present in pitticite. The name pitticite has validity only as a generic name for gel-like ferric iron arsenate minerals of varying composition.Yukonite is reported from the Sterling Hill mine, Ogdensburg, New Jersey, the second occurrence. New data for yukonite suggest the name should be retained.

ABSTRACT. The lead silicate minerals from Franklin, New Jersey, occurred in two separate assemblages. One of these is characterized by esperite associated with hardystonite and occasional larsenite. The second assemblage can be considered as two parts: one consists of margarosanite, barysilite, nasonite, and ganomalite; the other contains roeblingite and hancockite, together with a number of highly hydrated phases. Chemical analyses indicate that these species conform to their theoretical compositions. There are no simple lead silicates at Franklin; all are compound silicates of Pb with Mn, Zn, and Ca.