Geoscience Reference
In-Depth Information
have synthesized diamond artificially, as large as 0.5 mm, from charcoal. Though
the success of these experiments was treated as dubious, they certainly provided a
further stimulus for hydrothermal research, particularly the development of high-
pressure techniques. It is interesting to note that the results of some of these earlier
works were treated as dubious. This is probably in connection with the small size
of their resultant products. The first ever large-size crystals obtained by the earliest
workers were those of hydrated potassium silicate, which were about 2
3mm
long, by Friedel and Sarasin
[20]
. In this case, while growing orthoclase and feld-
spar, hydrated potassium silicate was obtained as an additional phase containing
surplus potassium silicate. Here, it is appropriate to quote one or two earlier experi-
ments for the curiosity of the readers and to show their experimental conditions.
Chroustshoff
[21]
obtained quartz by heating a colloidal solution of SiO
2
to 250
C
for 6 months. He started his experiments with 4 tubes, 3 of which soon burst. Some
cry
st
als
2
a
s
large
as 8 mm long and 3 mm wide quartz
crystals with
ð
faces were crystallized. Perhaps, this is the first sys-
tematic work on the growth of quartz. Although, the experimental duration was
quite long, almost 6 months, he could obtain quartz crystals as large as 8 mm long
and 3 mm wide. In another experiment, Chroustshoff
[22]
used a thick-walled evac-
uated glass tube of 25 cc volume, containing a mixture of colloidal SiO
2
solution,
colloidal Fe(OH)
3
, colloidal Fe(OH)
2
, lime water, freshly precipitated Mg(OH)
2
,
and several drops of a NaOH
1010
Þ; ð
1011
Þ;
and
ð
0111
Þ
KOH solution which he heated for 3 months at
550
C. The resultant product contained, among other things, long, thick, dark-
colored prismatic crystals of hornblende, 1 mm long, 0.5 mm thick, with (010),
(110), and (011) faces. The most interesting point to be noticed here is that the
experimenter obtained a mineral in 3 months under hydrothermal conditions having
no bearing on its petrogenesis and no relation to any known equilibrium. Morey
[23]
quotes this as a horrible experience of the experimenter. Here, the reader
should notice the duration of each experiment and the size and type of the minerals
obtained. This is definitely related to the lack of knowledge in areas of solvent
chemistry, kinetics, and solubility of the compound. Despite very low growth rates
achieved in the nineteenth century, the earlier workers in hydrothermal research
continued to synthesize a very wide range of mineral species. According to Morey
and Niggli
[24]
, over 80 mineral species are supposed to have been synthesized
during nineteenth century. The list includes quartz, feldspars, mica, leucite, nephe-
lite, epidote, hornblende, pyroxene of minerals from the silicate group, and several
nonsiliceous minerals like corundum (Al
2
O
3
), diaspore (Al
2
O
3
a
H
2
O), and brucite
(Mg (OH)
2
).
For the sake of convenience, the authors describe the further development of the
hydrothermal research in coherence with the autoclave design, development, and
pressure
temperature range. It is well known that the study of hydrothermal
processes is merely the study of certain aqueous systems at high temperature,
usually near to and often above the critical temperature of pure water; therefore,
considerable amounts of pressure are developed at these temperatures by water or
aqueous solutions. The experimental difficulties of such a study are many but are
largely connected with the choice and control of working conditions and the
