Monazite-(Ce) from a dolomite carbonatite at Kangankunde, Malawi, is sector
-zoned with variation in La2O3 of up to 6.0 wt.% and in Nd2O3 Of up to 3.9
wt.% between sectors. Single crystal X-ray diffraction, backscattered elect
ron imaging and microprobe analysis have been used to establish the relatio
nship between the morphology and sector chemistry of this low-Th monazite,
(Ce,La,Nd)PO4. Uptake of La by {011} sector surfaces is enhanced relative t
o that of {(1) over bar 01) and {100) sectors; Ce shows no partitioning dif
ferences; and uptake of Nd is more easily facilitated on {(1) over bar 01)
and {100) surfaces relative to {011). There appears to be a distinct relati
onship between the size of the REE ion and the probability of uptake via th
e different growth surfaces. Interpretation of this uptake behaviour, based
on theories involving 'protosites', involves an investigation of the possi
ble kink site geometries at edge-steps during growth. Part-formed kink site
s with small entrance sizes are calculated to occur with higher frequency o
n {(1) over bar 01} relative to {011}, and this con;elates with an increase
in the smaller-sized REE (Nd) uptake by {(1) over bar 01} growth surfaces.
The overall morphology and sector growth is suggested to be a function of
uptake chemistry.