2D. 
peridotite (Apollo 12), in lithic fragments (Apollo 14, LUNA 
20), and in a metamorphosed breccia (Apollo 16). Zirconolite is 
often associated with baddeleyite as small discrete crystals, no 
larger than 50um in diameter, and is considered to have 
crystallised at a late stage from interstitial liquids in the lunar 
basalts (e.g. Busche ef al., 1972). 
Lunar zirconolites are generally rich in Y and heavy-REE 
when compared with terrestrial zirconolites (Lovering & Wark, 
1974; Kochemasov, 1980; Fowler & Williams, 1986). The 
majority of the lunar zirconolites have EREE** > 50% of the Ca 
site, and with Y being the dominant REE, these may be 
considered as zirconolite-(Y). 
DISCUSSION AND CONCLUSION 
Zirconolite occurs as an accessory mineral only, generally less 
than 0.1mm in diameter, but from a wide variety of rock types. 
Its small size and low modal abundance means that it can be 
easily overlooked using traditional optical microscopy. 
However, with the increasing accessibility of analytical scanning 
electron microscopes (usually with a backscatter electron 
detector attached), zirconolite, even if present at a very low 
modal abundance, will be readily observed, because its 
backscatter component is considerably higher than the majority 
of the rock-forming minerals. It is probable therefore, that the 
number of zirconolite occurrences will increase significantly in 
the near future. 
It is also evident that zirconolite is often zoned, and/or finely 
intergrown with other minerals, and early bulk chemical 
analyses were unable to characterise fully the chemical 
variability of this mineral. Microprobe analyses, together with a 
detailed SEM investigation, is therefore essential in any study. It 
is generally recommended that microprobe analysis is performed 
using wavelength-dispersive means, because zirconolite can 
accommodate more than 30 elements at the 0.1 to 1.0 wt.% 
concentration level (which in energy-dispersive electron 
microprobe analysis is close to, or below, the detection limit), 
However, quantitative analysis of sub-micron zones has been 
successfully undertaken using an energy-dispersive analytical 
transmission electron microscope (Lumpkin et al., 1994). 
As can be seen from the data for natural zirconolite, the range 
of elements substituting, and the degree of substitution are 
extensive. The most commonly occurring elements, and 
therefore the minimum that should be reported in any 
microprobe analysis of zirconolite are: Mg, Al, Si, Ca, Ti, Mn, 
Fe, Y, Zr, Nb, Hf, Ta, W, Pb, Th, U and of the REE, La, Ce, Pr, 
Nd, Sm, Gd. 
It should also be noted that Cr and Zn are present in some 
zirconolites: Cr predominantly from lunar samples, and Zn 
occasionally from metasomatic samples (e.g. Zakrzewski et al., 
1992). H,O has been reported in wet chemical analyses of 
separated grains (e.g. Borodin et a/., 1960; Bulakh et al., 1960), 
and has also been inferred from low analytical totals of 
microprobe data (e.g. Platt et al., 1987; Zakrzewski et al., 1992). 
Na and K, although also quoted in some wet chemical analyses 
of separated grains, have not been observed in microprobe 
analyses. It is probable therefore, that Na and K are not present 
to any significant extent in zirconolite. It is of note also, that Sr 
and Ba generally do not occur in natural zirconolite, and Pb only 
rarely does so. These elements might have been expected to 
substitute more readily for Ca, but it appears that the Ca 
C.T. WILLIAMS AND R GIERE 
structural site does not easily accommodate 2+ cations larger 
than Ca. The valency state of Fe in zirconolite is unclear: where 
measured directly on mineral separates, both FeO and Fe,O, are 
present. 
It is evident that zirconolite, although invariably occurring 
only as an accessory or ‘trace’ mineral in a range of rock types, is 
able to accommodate many incompatible elements, such as © 
REE, ACT, Nb, Zr, Hf, Ta to concentration levels whereby it can 
become a major repository for these elements. As such, it has the 
potential for playing a _ significant role in the 
petrological/geochemical evolution of those rock-types in which 
it crystallizes. Several studies have provided evidence that | 
zirconolite can reflect changes in the composition of the fluid 
during its evolutionary history, both in metasomatic systems - 
(Williams & Gieré, 1988; Gieré & Williams, 1992), and in 
magmatic fractionation processes (Platt et a/., 1987). 
It is hoped that this review and compilation will prove useful | 
as a comparative database for geologists who discover 
zirconolite in their samples, and also to material scientists 
working on various SYNROC projects, in order that they can 
compare laboratory-based experiments on synthetic zirconolite 
with studies of the natural forms of zirconolite. 
This database is available in a computerised format from | 
CTW. We would be grateful also to receive any additional | 
analytical data and/or material from new occurrences of 
zirconolite, in order to periodically update this database. 
ACKNOWLEDGEMENTS. We are very grateful to Professor G. Bayer (ETH, | 
Zirich) for providing us with zirconolite samples from Phalaborwa, and — 
also for some unpublished data, to Alf Olav Larsen (Porgrunn, Norway) | 
for samples from Langesundfjord, to Dr. S.L. Harvey Edinburgh, 
Scotland for providing information on zirconolite from East Antarctica, 
to Professor J. Keller (Freiburg, Germany) for permission to analyse 
zirconolite from Hegau, to Dr I. Hornig-Kjarsgaard (University of 
Mainz, Germany) for allowing us to include her unpublished data from 
Sokli, to Professor J.B. Dawson (Edinburgh, Scotland) for unpublished | 
data, to Dr E.S. Grew (University of Maine, USA) for providing 
material from Ser Rondane, Antartica, to Dr. A.N. Mariano (Carlisle, 
Massachusetts, USA) for providing samples and information on several 
zirconolite localities, and for some unpublished data, to Dr G.C. Parodi 
(University of Rome, Italy) for samples from Latium, Italy, and to the | 
Kovdor Mining Museum, Kola Peninsula for material from Kovdor. We l 
further wish to thank Drs M. Welch, A.R. Woolley and R.F. Symes and | 
other colleagues at The Natural History Museum, London, also to | 
Professor Andrei Bulakh (University of St. Petersburg) for comments | 
and suggestions which have improved the manuscript, and to Greg | 
Lumpkin (ANSTO, Australia) for discussions regarding synthetic | 
zirconolite. This study forms part of a British/Swiss Joint Research | 
Programme, and we gratefully acknowledge funding provided by the | 
Schweizerischer Nationalfonds and the British Council (Grant No. 
83BC-033381). 
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A.A. 1988. A system of nomenclature for rare-earth mineral species: revision 
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, Mazzi, F., Munno, R. & White, T.J. 1989. Mineral nomenclature: zirconolite. 
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