Jökull - 01.12.1976, Side 34

Fig. 2. Differential thermal analyses of clay
samples from Reykjanes. Run in air. Heating
rate approx. 10°C/min. Sample weight about
1 g-
Minerals Drill- Depth
hole m
1 Smectite 4 218
2 Mixed-layer mineral 4 578
3 Mixed-layer mineral and
swelling chlorite 8 664
4 Mixed-layer mineral and
swelling chlorite 2 and 5 . .. 8 1100
5 Smectite-f-swelling chlorite 4 4 776
6 Swelling chlorite 2 8 1708
7 Chlorite 1 and swelling
chlorite 4 8 1604
Mynd 2. Mismunur á hitastigi leirsýna frá
Reykjanesi og sýna af áloxiði, sem hituð eru
samtímis með jafnri upphitun. Aloxiðið hitnar
upp jafnt og þétt við aukið hitastig, en í leir-
sýninu verða strúktúrbreytingar í kristöllunum
og efnahvörf, sem koma fram i því, að hitastig
helst óbreytt á meðan, eða hækkar örar en í
áloxiðinu.
and gradual changes found in the thermal be-
haviour of the minerals are rather in contrast
to the often quite different X-ray patterns for
some of the minerals and their different swell-
ing abilities and spacing after heating. Even
though gradual changes from the thermally
stable to the thermally instable varieties were
sometimes observed by X-ray diffraction, two
well defined groups were found according to
the swelling abilities. The DTA patterns of
the smectites (Fig. 1) show a strong endo-
thermic peak at 160 °C and another at 195—
230 °C. The third endothermic peak at about
560 °C is considered to be the result of be-
ginning interlayering of the smectite by “chlori-
tic” layers (Mackenzie, 1957, a, b). The curves
for the smectites are similar to curves for iron-
rich saponites (Sudo, 1954, Miyamoto, 1957).
One sample was run of the strongly swelling,
thermally instable mineral, chlorite 5, and it hacl
a pattern rather similar to the smectites, but
no defined peaks were recorded at temperatures
above 600 °C.
According to the DTA results the clay
minerals change from smectites, slightly inter-
32 JÖKULL 26. ÁR
layered with brucitic interlayers, to structures
containing some interlayer water but with
brucite interlayers dominant. The relative
amounts vary however considerably. The de-