Polydetrital Urasite

Urasite has been described by Grunt in the seventh volume of his "Synthetisch-chemische Wachstumanalyse" as the progenitor of all known polydetrital forms. It occurs as botryoidal deposits, of a character aptly described in the Russian literature as bosominous, along the lower bottoms of the Dnieper. Similar deposits have been found, in conjunction with marsupial intergrowths of columbrite and hyasakite, in the Belltel salt mines, near Murray Hill, Iowa; and Penrod reports paunchy developments with maulzite in Chicken Creek, Saskatchewan.

Chemically, urasite is a basic irium salt of uridic acid, and is one of the aphides to which Professor J. D. H. Fingalscave directed our interests recently in Nature. As usual, a great deal of the fundamental work on this material has been done in England. Since the chemistry is quite unclear, however, and the morphology and structure are completely unknown, the series presents a challenging problem to us. The neutron, iridium, and deuterium salts, known to mineralogists as makalite, stahtafite and chronkite respectively, are so similar in nature that we need say no more about them.

Polydetrital forms were first described by Heinrich Zundt, and perhaps the best-known example of the form has been thought to be zundtite, named for that investigator. Actually, our studies tend to show that this mineral is not representative of the polydetrital classification at all, however, the appearance of zundtite under the microscope being due to pyloric etching. I say our studies; but I must point out that the whole subject of polydetritalism has been clarified chiefly by the keen analysis of our retiring president, Professor M. J. Buerger, through his definition of the coefficient by means of which the form can be characterized. The occurence of this form in estrogenic soaps is responsible for Buerger's interest in the subject.

Buerger has shown that when a polydetrital form is examined under the precessing petrographic microscope, and preferably by means of the nine-axis Fetherow stage, the angle between any two adjacent detrital faces always lies between some integral multiple of + or - 2(π + δ), where δ → ∞. This observation is true regardless of the crystal class to which the material belongs; and it proves to be the key to the classification and indeed to our understanding of the forms. This integral multiplier of the inter-detrital angular range we have designated as the Buerger** factor.

We have examined all the polydetrital forms reported in the literature, and many more not so reported. In our survey of these minerals, it has proved useful to add a servo-motor drive to our universal stage, and to employ a television pickup for angle recording. It is now possible simply to place

The remarkable aspect of this tabulation is the large negative Buerger factors associated with urasite and its related salts. This prompts the assignment of the term dia-ferro-polydetritalism to this mineral group. Since, as is rather well known, polydetritalites are semi-dimensional extensions of two-dimensional forms, the very large negative factors are explainable only in terms of Donnay-Hilbert coordinates. I shall refrain from a mathematical discussion at this time, and refer you to the coming ASXRED monograph on the subject by M. J. and N. Buerger, G. Hambuerger, J. Lukesh, I. N. Klein and Y. Snodgrass.

In closing, I should like to present a few of the more prominent entries in our table. The entries are in order of ascending absolute magnitude of Buerger factor, and special emphasis must be placed on the signs. You will note with approval that zundtite, now known to be non-polydetrital, is omitted from the list.

In closing, I am delighted to acknowledge our indebtedness, in this clarifying classification of polydetritalites, to our retiring president, Professor Buerger, without whose inspiration this contribution would not have been possible.

This development was not supported by the Office of Naval Research.