Geoscience Reference
In-Depth Information
Figure 8.16 Photographs of the alkali rare earth tungstates
[53]
.
more in experiments with pH values varying from 8.0 to 9.0. The pH of the mineral-
izer and the % fill have a considerable influence on the morphology and growth rate
of NaLa(WO
4
)
2
crystals. With an increase in the pH of the system, the morphology
varies from well-developed bulk crystals of pseudolower symmetry to long needles of
even 7 mm long in an experimental run, often of days. Similarly, with an increase in
the pressure of the system, the morphology varies from needles (at lower pressure con-
ditions) to bulk crystals of pseudolower symmetry (at moderate pressure conditions);
thus, the hydrothermal growth of tungstates, particularly alkali rare earth tungstates,
carries a great significance in hydrothermal research.
8.8 Hydrothermal Synthesis of Molybdates
There are not many molybdenum bearing minerals in nature, and the most important
mineral is wolfenite, PbMoO
4
, belonging to the scheelite group. Hence, molybdates
