Clay Minerals (1967) 7, 101.
THE ARGILLATION
FROM
OF SUB-MARINE
THE MOUNT
CARMEL,
TUFFS
ISRAEL
ARIEH SINGER
Soil Science Department, Faculty o[ Agriculture, P.O.B. 12, Rehovot, Israel
(Received 24 October 1966)
ABSTRACT: The alteration products of five sub-marine tufts from the
Mount Carmel were analysed chemically, by X-ray, D.T.A. and I.T.A. techniques
and their mineralogical composition determined. Smectites are dominant in all
the samples. In the less altered tufts the smectite seems to consist of a mixture
of saponite with a smecfite from the beidellite-nontronite series. In the more
intensely altered tufts the saponite disappears and a swelling chlorite appears.
The formation of the swelling chlorite is attributed to the degradation of the
saponite. These mineralogical changes are accompanied by the loss of a large
part of the alkali and alkaline earth cations.
INTRODUCTION
The regions of the Near East were subjected to several phases of volcanic activity,
the latest of which took place during the Neogene and extended into the Pleistocene.
It gave rise to extensive lava fields covering parts of Galilee in Israel and
other regions in Syria and Lebanon. During the Cenoman-Senon period a phase
of volcanic activity of much more limited extent occurred in the Mount Carmel
region. It had no parallel in other regions of Israel or the Near East and deserves
special attention on account of its particular mode of manifestation.
Mount Carmel, situated to the south of the city of Haifa (Fig. 1), is separated by
a narrow shore-line from the Mediterranean Sea, and was formed by an anticlinal
uplift of Cenomanian, Turonian, and Senonian strata consisting mainly of
dolomite, limestone, chalk, and marl. Series of volcanic rocks composed in the
main of basaltic tuff, accompanied by some basaltic lava flows, form local intercalations of varying thicknesses in the sedimentary calcareous formations. Sass
(1957), in a study of the volcanic phenomena of Mount Carmel, believes the
volcanic eruptions to have taken place under sea level and classifies the tufts,
according to their morphological appearance, into three groups: (a) black tufts,
massive and compact, which form the base of the tuff sedimentary series, and
are situated nearest to the volcanic outlets. The black tufts are coarse grained,
with ~the original primary mineral composition (mainly volcanic glass) largely
102
Arieh Singer
150
140
I60
t70
250
HAIFA /
240
P gJ
....:,~-~.
"- ~ ..r-.~ ~ \ \
to
",
--
??
.
.
)
~>
Muhraka
240
~T
4~
Ofer~
3
~
~.~.
Q
.
220
/
210
-
oQisaryo
.
"~..
%, 9.,..
J"
,.~..t"
/
Scale
: 1:250.000
Fro. 1. Schematic location m a p of M o u n t Carmel.
The argillation of sub-marine tuffs from Mount Carmel, lsrael
103
preserved; (b) variously coloured tufts (red, green, grey or yellow) which appear in
layers and are above the black tufts. The variously coloured tufts appear in all
grain sizes and are largely altered; (c) yellow tuff layers forming the top of the
tuff sedimentary series and having the greatest radius of spread. These tufts also
appear in all grain sizes and are very strongly altered.
While the alteration products of volcanic glass transported into a marine environment have been amply investigated in many places in the world, reports on
alteration following sub-marine eruptions are very rare. It was therefore thought
worthwhile, in the course of a study on the alteration of volcanic material in Israel,
to analyse the Mount Carmel tufts.
A large number of tuft samples were examined with X-ray and D.T.A. techniques
and five samples representing the various stages of alteration were subjected to
more detailed mineralogical and chemical analysis:
Kerem Maharal A. Black tuft; no layering visible; coarse grained; vesicular, with
part of the vesicles filled with calcite.
Kerem Maharal B. Yellowish-brown tuft, from a layer about 2 m thick; coarse
grained.
Kerem Maharal C. Greenish-brown tuft, from a layer about 1.5 m thick; fine-grained,
vesicular.
Ofer A. Yellow tuff; from a layer several metres thick; fine grained.
Ofer B. Soil formed from uppermost part of Ofer A yellow tuft.
EXPERIMENTAL
PROCEDURE
One thousand grammes of each air-dry sample were crushed to pass through a
210 /L mesh sieve. The organic matter in the material was destroyed with H2Oz.
The chemical composition, after fusion, was determined according to the conventional system of silicate analysis. The differential dissolution analysis (D.D.A.)
technique of Hashimoto & Jackson (1960) was used to estimate the amounts of
amorphous Si, while amorphous Fe and A1 oxides were removed by the Aguilera
& Jackson (1953) method from samples saturated with Na. Fe was then determined
with ortho-phenanthroline and A1 with pyrocatechol (Wilson & Sergeant, 1963).
The C.E.C. was determined using ammonium acetate as replacing agent.
Mineralogical determinations were made using a D.T.A. apparatus with photographic recording and a furnace heating rate of 10 ~ C/min, and a Philips X-ray
apparatus with Co-Ka radiation. Both oriented and unoriented samples were used.
Samples preheated to 500 ~ C and others saturated with glycerol were also examined.
I.T.A. was carried out with a Stanton 1 mg thermobalance (I.T.A.--isothermal or
thermogravimetric analysis).
RESULTS AND INTERPRETATION
Sample Kerem Maharal A
The coarse grains of this sample, representing the 'black tufts', were found to
consist of a central, black zone, containing unaltered, sideromelanic, volcanic glass.
Arieh Singer
104
The unaltered volcanic glass was always embedded in a yellowish-white material,
which, upon X-ray analysis, proved to contain a well-crystallized smectite, accompanied by calcite. Numerous small vesicles were filled with the same material.
Difficulties in the separation of the smectite prevented its more detailed chemical
analysis. The high hygroscopic moisture content in the overall chemical composition
of the tuff (Table 2) is caused by its partly altered condition. All other tuff samples
were found to contain only secondary minerals in the form of clay, with no remnants
of volcanic glass.
Mineralogical analysis of samples Kerem Maharal B and C, Ofer A and B
X-ray. All the clays examined gave the reflections characteristic of smectite-type
minerals. The 001 reflection of dry, unoriented powders expanded upon orientation
and glycerol saturation to 17"8 A (Table 3). Integral series of basal reflections
indicated absence of random interstratification. A fairly strong 060 reflection at
1-534 A was always observed, showing the presence of a trioctahedral mineral
(Table 3). A fainter reflection at 1"504 A may have been due to the superposition
of a basal reflection on a second 060 reflection. Sharp and symmetrical reflection
lines in the Kerem Maharal B sample clay indicated good crystallinity. In the clay
samples from Kerem Maharal C and Ofer A and B reflection lines were less sharp,
and background scattering more intense. In the clay samples from Ofer A and B
the 001 reflection line in oriented and glycerol saturated samples had the form of
a narrow, diffuse band, extending towards smaller spacings.
Upon heating the samples to 500 ~ C for 2 hr, only the Kerem Maharal B sample
TABLE1. Chemical composition of clays
SiOz
A180a
FezO3
FeO
TiO2
P~O5
CaO
MgO
Na~O
I(20
Ign. loss
Total
C.E.C. (m-exl/100g)
Amorphous SiOz
Amorphous A1203
Amorphous Fe~O8
Kerem
Maharal B
Kerem
Maharal C*
Ofer A*
Ofer B
37.44
10.69
12-58
0.22
2"40
1"08
4-90
7"90
0'08
0 "04
23.20
100"53
115'0
4.90
1.60
1.65
41.64
14-41
8-38
0
2"95
1"21
4-00
4.00
0'26
0-32
22.87
100-04
95-0
5"36
2-00
2'50
40.70
14.62
8-51
0
1"97
0"94
4"00
5-19
0"11
0.04
23.77
99.85
110.9
2-10
1.80
2.00
41-00
14.91
10-34
0
2.11
0"70
4"93
3"39
0"18
0-10
22.40
100.06
109"8
3.00
2-10
6.50
*Calculated on a lime-free basis.
The argillation of sub-marine tuffs from Mount Carmel, Israel
105
TABLE2. Chemical composition of partly altered tuff, basalt and volcanic
bomb samples
Basalt*
Muhraka
SiO2
A1208
FeO
Fe203
TiO,
P205
CaO
MgO
Na20
K20
H20H20 +
lgn. loss
Total
46.19
13.16
8.02
4-18
3 "48
0.57
9 "40
7.16
2.65
0.83
1.47
2-63
99.74
Tuff~
Kerem Maharal A
39"03
11.62
1.51
11"43
2"66
0.92
5.29
11.72
0.55
1.00
13.94
99.67
Volcanic bomb*
Kerem Maharal
37-92
11"37
4'05
9"05
3"03
11"20
12.40
-0.20
2.96
7.81
99.99
*After Sass (1957).
tCalculated on a lime-free basis.
showed complete collapse of the 001 reflection to 9"6 A. In the other clays, together
with a diffuse band at 9-6 A, a second line in the form of a diffuse band appeared
at 12"6 A. This band was strongest in the samples from Ofer A and Ofer B.
In all the clay samples examined, reflections from apatite and calcite were also
present.
D.T.A. and I.T.A. Two endothermic peaks were obtained in the D.T.A. of all
clay samples, one at 150 ~ C representing adsorbed water, and a smaller o n e at
880 ~ C, followed immediately by a very small exothermic peak.
Sample Kerem Maharal B, exhibiting these features only (Fig. 2, curve a),
resembles very much the curve obtained from the Krugersdorp, Transvaal, saponite
(Schmidt & Heystek, 1953), the only difference being the relative size of the hightemperature peak. The loss in weight, large and abrupt between 100 and 300 ~ C became afterwards very slight and gradual, its rate increasing only somewhat between
500 and 700 ~ C (Fig. 3). The high temperature endothermic peak was not accompanied by any noticeable change in weight, but seemed to be directly related to the
content in MgO, confirming the observation of Page (1943).
In the clays from Kerem Maharal C and particularly in those from Ofer A and
Ofer B, in addition to the endothermic peaks at 150 and 880 ~ C, a small endothermic peak was observed in the region of 580 ~ C (Fig. 2, curves b, c, d) which
was accompanied by a weight loss of about 2-5 %.
Both X-ray and D.T.A. results suggest that the clay from Kerem Maharal B
is composed of a smectite with relatively few impurities. The high temperature
peak in the D.T.A., as well as the 060 reflection of 1-534 A in the X-ray analysis,
Arieh Singer
106
9
~
ar I.
9
r~
Z
++
f~d
<
9
o
e~
<
o~
o
t~
C3~
The argillation of sub-marine tufts from Mount Carmel, lsrael
107
suggest a saponite-type mineral. However, the high amount of ferric iron (Table 1)
cannot be accounted for in a saponite and also not in the iron-rich varieties cardenite
(MacEwan, 1954) and grilfithite (Faust, 1955), particularly when the high exchange
capacity is taken into consideration. An iron containing smectite must therefore
also be present. Calculating the amount of saponite on the basis of 100%
saponite = 27% MgO (average from the analyses of two iron-free saponites quoted
by Deer, Howie & Zussman, 1962), 41% of saponite was obtained, The SiO=, A1208,
and FezO~, not required for the saponite, give a smectite of beidellite-nontronite series with the approximate formula: Ca0.45Mg0.09Nao.01K0.01(Si6.00All.~o)
(All.20Fe++%8o) 020 (OH)4. The Kerem Maharal B clay can therefore be considered
as consisting mainly of a mixture of a saponite with another smectite of the
beidellite-nontronite series.
In samples Kerem Maharal C and particularly in samples Ofer A and Ofer B
the incomplete expansion following glycerol saturation and only partial collapse
after heat treatment suggest that the Mg is present in a pseudo-chloritic structure.
Also the appearance in the D.T.A. curves of a slight endothermie reaction in the
500-600 ~ C region accompanied by a small loss in weight point in the same
direction, being indicative of the presence of a brucite layer. The curve also resembles
somewhat that obtained for a swelling-chlorite by Honeyborne (1951). Caill~re &
(a)
_
~
Cb)
AT
~
~-~
I
I
tO0
200
,
"~
~
I
I
300
400
500
600
Temperature (~
i,,
(d)
I
I
I
700
800
900
FIG. 2. Differential thermal analysis curves of tuff samples crushed to pass a 210 tz
mesh sieve. (a) Kerem Maharal B; (b) Kerem Maharal C (the large endothermic peak
at 900 ~ C is due to the presence of calcite); (c) Ofer A (contains calcite impurities);
(d) ofer B (small endothermic peak at 280 ~ C is due to the presence of poorly crystallineamorphous iron hydroxides).
Arieh Singer
108
24
~- 2 0
._m
c
16
l//
_9o
/
I00
- . . . . .
t
ZOO
I
500
I
400
I
500
I
600
Ofer B
Kerem Maharal
I
7'00
1
800
I
900
B
I
JO00
Temperature ( ~
FIG. 3.
T h e r m o b a l a n c e traces o f tuff samples. T h e t e m p e r a t u r e was increased by
increments o f 7 ~ C every minute.
H6nin (1949) prepared an artificial pseudo-chlorite by precipitating Mg(OH)2
between the sheets of a montmorillonite from Camp Berteau. Using their figure
for the content of MgO as a basis for the calculation of the amount of pseudochlorite in the Mount Carmel samples, 27-5, 35-6, and 23"0% for Kerem Maharal
C, Ofer A, and Ofer B, respectively, were obtained. The SiOz, A1202, and FezO~,
not required for the pseudo-chlorite, give a smectite with the approximate formula:
Cao~2Mg0.05Na003K00~ (Si7.63A10.37)(All.92Fe+++l.s~)020 (OH)4. The high exchange
capacity of this smectite is caused by the vacancies in the octahedral layer.
Samples Kerem Maharal C, Ofer A, and Ofer B seem to be composed mainly
of a mixture of a smectite with a pseudo-chlorite (swelling chlorite).
DISCUSSION
In order to interpret the alteration processes which resulted in the present
mineralogical composition of the Carmel tufts, the composition of the original
unaltered material has to be known. However, no tuff samples were found which
were completely fresh. Sass (1957) gives the chemical composition of relatively
unaltered basalt found accompanying the tuft deposits and also that of a volcanic
bomb (Table 2). The difference in their chemical composition he attributes to
different parent magmas. From the data it is seen that tuff sample Karem Maharal
A, which is relatively the least altered, has also a chemical composition which is
nearest to that of the volcanic bomb and it is probable that both originate from
the same parent magma. The chemical composition of the volcanic bomb can therefore be accepted as representing the original composition of the unaltered volcanic
glass.
If, as is postulated by Sass (1957), the volcanic eruptions were sub-marine, the
first and probably most potent environment with which the erupted ash came into
contact was that of sea-water. The principal alteration products considered to have
The argillation of sub-marine tufts from Mount Carmel, Israel
109
been formed from volcanic glass in a marine environment are the various bentonites
widely described in literature. With some exceptions the great majority of the
bentonites are Ca- smectites belonging to the montmorillonite-beidellite series.
Conditions cited (Hauser & Reynolds, 1939; Grim, 1953) as favourable for the
formation of montmorillonite from volcanic glass are stagnant, alkaline water and
the availability of ions of Mg, Ca, and Fe. However, the alterations undergone
by the Carmel tufts are not exactly analogous to those which produced most of the
bentonites. The environment of a submarine eruption accompanied by the formation
of high-pressure zones and emanation of hot gases, can more correctly be compared
to that when hydrothermal alterations take place. Hot spring activity in an alkaline
lake was reported by Sand (1957) to produce saponite from tuff. The amount of
saponite is by necessity limited by the amount of Mg present in the tuff since it
seems probable (Powers, 1959) that external sources of Mg (like sea-water) would
lead to the formation of brucite layers and to a chlorite or swelling chlorite clay
mineral.
Volcanic glass is known to contain tetrahedrally coordinated A1 and Egawa
(1964) has shown experimentally that allophane, a common alteration product of
volcanic glass, contains AI in the four-coordinated state. Milliken, Mills & Oblad
(1950) have shown for Si-Al-hydrogels that tetrahedrally coordinated A1 is stable
in the presence of an excess of tetrahedrally coordinated Si. Since this condition
pertains in the case of the tufts, a process may be envisaged, caused by an alkaline
hydrothermal environment a.cting on unaltered volcanic glass by which initial
hydration and physical breakdown (palagonitisation) of the volcanic glass is followed by removal of a large part of the alkali and alkaline earth cations. Simultaneously, a structural rearrangement of the basic building units of the volcanic
glass may take place by which all the Si and most of the A1 in four-coordination
and the Mg, Fe, and some of the A1 in six-coordination rearrange to form sheets.
The strain energy shown (Ewart & Fieldes, 1962) tO be contained in glass may have
a part in triggering oft this process.
Clay sample Kerem Maharal C exhibits a somewhat different aspect. The Mg
is present here in a swelling chlorite-like mineral instead of in saponite. Also more
of the Mg and probably all of the Fe ++ have been removed. These changes are
associated with the porosity and fine grain size of the tuff which served as parent
material for this clay. Fine grain size and porosity must have greatly increased
the effect of sea-water. Some of the Mg removed from the mica-layers of saponite
may have been reprecipitated in the form of a brucite layer and thus a chlorite-like
structure obtained, similar to the product obtained artificially by Slaughter &
Milne (1960) from montmorillonite by the action of solutions of Mg(OH)2 and
AI(OH)a. Mixed-layer montmorillonite-chlorite found by Grim & Vernet (1961) in
altered volcanic ashes near the island of Capri, is believed by the authors to
have been formed from the rapid degradation of montmorillonite.
Sample Ofer A represents the alteration undergone by one of the latest tuff
showers, situated on the top of the tuff sedimentation series. Since this tuff layer
was not covered immediately by subsequent tuff layers, this material must have
110
Arieh Singer
been for a relatively long time in contact with sea-water, that is, until enough
carbonates formed to cover it with a protective mantle. Here also the effect of
prolonged activity of sea-water on tuff is seen to produce a swelling chlorite.
T h o u g h Powers (1957) and Carrol & Starkey (1958) found that Mg f r o m the
sea water moves preferentially into the exchange positions of montmoriUonite and
that this process m a y ultimately lead to the formation of chlorite in deeply buried
sediments, no external M g seems to have contributed to the formation of the swelling
chlorites in Kerem M a h a r a l C and Ofer A tufts. It is more likely that the formation
of this mineral is the result of the degradation of a saponite-like smectite formed
initially.
As the analysis of sample Ofer B shows, meteoric weathering conditions do not
seem to have had a great additive influence on the alteration of the clay. The only
appreciable effect of the climatic conditions of the Mediterranean zone seems to
have been an increase in the proportion of iron present in the a m o r p h o u s state
(Table 1) and the leaching of lime from the uppermost layers. T h e great adsorptive
capacity of the clay for water probably impedes the leaching to such an extent that
rainfall is not sutticient to cause any further alterations.
ACKNOWLEDGMENTS
The author wishes to express his appreciation to Mrs V. Cosman of the Faculty of Agriculture,
Rehovot, for her precious aid in the mineralogical analyses, and to Mr R. Herschhoru for
carrying out some of the chemical work.
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