Management of Commercially Generated Radioactive Waste - U.S. ...

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Koreskawa 1954) and differential thermal analysis (DTA) (Kerr and Hollan 1951, Orcel 1953,
Kurath 1957). Most of the effort by mineralogists has been directed at establishing identi-
fication criteria.
Elemental analysis is commonly completed by wet chemical means on mineral separates or
by standard electron microprobe analysis. The presence of water, both structural and
absorbed, and the preponderance of rare-earth elements make a complete chemical analysis a
rarity in the literature.
Although radiation damage experiments are voluminous, there have been only limited and
unsuccessful efforts to simulate the process of metamictization under laboratory conditions
(Mugge 1922, Primak 1954).
P.4.2 Summary of Observed Metamict Phases
To understand the compositional and structural controls on the process of metamictization,
it is useful to tabulate naturally occurring metamict phases. Table P.3.2 listed
those phases described as being partially or completely metamict in a review of the litera-
ture by Bouska (1970). This tabulation lists only the major compositional end-member. As
one might expect for mineral groups of complex compositions (e.g., compare the A:B ratios
for fergusonite and samarskite) that are metamict and much altered, the nomenclature of any
single mineral group is quite complicated and much confused by the proliferation of varie-
tal names (Ewing 1976). For a more detailed listing and discussion of the mineralogical
literature the reader is referred to Bouska (1970).
The asterisk by each mineral name indicates it also occurs as a partially or completely
crystalline phase. In some cases (e.g., monazite, xenotime and vesuvianite) the inclusion
of a mineral phases as metamict is based only on a single or poorly documented occurrence.
In these instances the critical reference is indicated. In other cases (e.g., rutile) the
radiation damage was not caused by constitutent uranium and thorium nuclides but rather
occurred only along grain boundaries where the rutile was in epitaxial contact with radioactive
davidite.
The uranium and thorium contents of phases that occur in both crystalline and metamict
forms are interesting. Table P.4.1 gives the average U 30 8 and Th0 2 contents of orthorhombic
AB20-type Nb-Ta-Ti oxides. Although the data in the literature are limited, in general
those specimens of euxenite, fersimite, aeschynite and lyndochite found in the crystalline
state have distinctly lower uranium and thorium contents than their metamict euxenite and
aeschynite counterparts. A similar relation has been demonstrated for zircons (Holland and
Gottfried 1955, Krasnobayev et al. 1974).
Table P.4.2 is a compilation of radioactive minerals which are said to be always crys-
talline. Comparison of Tables P.3.2 and P.3.4 quickly reveals inconsistencies in the literature.
Huttonite is listed as always crystalline (Pabst 1952) and partially metamict
(Bouska 1970). Many of these inconsistencies may be resolved by very detailed and specific
examinations of nomenclature. Also, note that among the phases listed as metamict (e.g.,
columbite and stitbiotantalite), their structures probably will not accommodate either