Jökull - 01.12.1976, Page 35

TABLE 1
Classification of the clay minerals from Reykjanes based on X-ray data
TAFLA 1
Flokkun leirsteinda frá Reykjanesi á grundvelli röntgengreininga. I töflunni er sýnt, hvernig
þykkt (001) lagflatanna breytist við mettun með ethylenglycol og við hitun við 600 °C. Einnig er
sýnd þykkt (060) lagflatanna.
Mineral d(001) in Á at 35% rel. moist. d(001) in Á glycolated d(001) in Á after heating at 600 °C d(060) in Á
Smectite 12.3-15.3 16.9-17.1 9.6—9.9 1.53
Mixed layer mineral of
chlorite/smectite 14,0-14.6 15.3-15.7 12.3-12.9 not recorded
Chlorite
1 14.0-14.6 14.0-14.6 13.9-14.0 1.53
Swelling chlorites
2 14.0-14.6 15.0-15.5 13.9-14.0 1.53
3 14.0-14.6 15.0-15.5 none 1.53
4 14.0-14.6 16.5-17.0 13.9-14.0 1.53
5 14.0-14.6 16.5-17.0 none —
hydroxylation of the minerals with imperfect
brucite interlayers occurs at slightly lower
temperatures than normal for chlorite. The X-
ray diffraction results indicated a structural
difference dividing the “swelling chlorites” in-
to two groups of swelling abilities. This differ-
ence has no effect on the thermal behaviour.
Swelling chlorites 2 and 4 have framework and
brucite layers stable enough to remain after
removal of the considerable amount of “struc-
tural bouncl” water found to be in the minerals.
The brucite layers are either flexible enough
to permit a double layer of an organic liquid
to diffuse in between the layers or only one
layer can get in. The chlorite 2 group (Table 1)
could possibly be a mixed-layer structure of
swelling and non-swelling chlorite. According
to X-ray results the thermally instable “swell-
ing chlorites” could as well be interpreted as
thermally instable smectites (chlorite 5) and
mixed-layer smectite/chlorite minerals (chlorite
3). The DTA data for those minerals are limit-
ed, but they rather support the latter explana-
tion.
STUDY OF THE INFRARED SPECTRA
The infrared spectra of several of the clay-
fraction samples from Reykjanes was investigat-
ed. The clay minerals give rather broad ab-
sorption bands. This seems to be a general
feature of the finegrained and often poorly
crystallized clay minerals from altered rocks in
Icelandic geothermal fields (Kristmannsdóttir,
1975). The OH-region of the infrared spectra
for some of the samples is shown in Fig. 3 and 4.
The smectites show normally a broad “trough”
in the OH-region and no well defined absorp-
tion bands. Some show two poorly defined
peaks within the “trough” at approx. 3600 and
3380—3400 cnr1. The “trough” is retained
after heating at 400 °C, but becomes lower,
still worse defined and is at lower frequency.
Samples containing chlorite 5 have spectra very
similar to the smectites. Close similarities are
found for the spectra of all chlorites, chlorite
mixtures and the mixed-layer minerals. The two
main absorption peaks occur in all at 3560 and
3400 cnr1. Those values are as recorded for Fe-
JÖKULL 26. ÁR 33