GEOL. CROAT. 50/1 17 - 25 7 Figs. 2 Tabs. ZAGREB 1997 

Glauconitic Materials from Lower Miocene Macelj-Sandstones of the 
Hrvatsko Zagorje, North-Western Croatia 

Neven TADEJ, Dragut in SLOVENEC, Josip TISLJAR anci [vica INKRET 

Key words: Macc lj -sandslones, Gl auconitic mate rials, 
G lauconite, XRD powder patte rns, Chemical com­
pos ilion, Thermal analysis, I-Irvatsko Zagorjc, 
Cremia. 

Abstract 
The Lowe r Mi ocene Macc lj -sands[OIlCS, from (ile western part of 

Hrvatsko Zagorje, arc green in colour with variabl e amounts o f glau­
conit ic gra ins. Thi s paper presents the results of mineralogical and 
some petrological ana lys is of three char:lClcris tic sam ples of these 
sandslones. 

The natura l sandstone sampl es were ana lysed by polarisi ng 
microscope and by X -ray powcler diffraction (X RD). A fter separation, 
the pure or ,\hnos( pure g lauconitic material s were analysed by XRD, 
chemi c,\1 ililal ys is and th enn;11 analysi s (TG , DTA and DTG). The 
res ults show variati on, not onl y in (h e gl au conit ic mat erial of the 
sandstone samples. but a lso within individ U<ll samples. The amount o f 
smeclite layers varies fro m < 5% to approximatel y 40% de pendi ng on 
the degree of order and the stage of gl<lllconilc cvolution. Th is is indi ­
cated by th e contents o f K, AI, Fe , ad sorbed water and cat ion 
exc hange capacity as well as XRD powder palle rns. 

1. INTRODUCTION 

T he Macclj -sand stones arc located in the wes te rn 
pari o r th e Hrvat sko Zagorje reg ion in north -weste rn 
Croatia, and in adjacent eastern Sl ovenia. Th e nam e 
Macclj -sandstoncs has been lIsed ever since they were 
desc ri bed by GORJ ANOVIC-KRAMBERGER ( 1904) 
in the ex planatory tex t for the geological map. sheet 
Rogat cc-Kozje. as "g recnish-grey turfaceou s sand­
stones indicating a shallow -marine environm ent". 
These sand ston es o lli c rop in th e Hrvatsko Zagorje 
region be tween Mt. S trahinsciea and MI. Ivansc iea in 
the south, and Mt. Ravna Gom in the north, covering a 
tota l surface area of about 130 km2 (Fig. 1). This rorl1la ~ 
lion is prcdominantly com posed or shallow-marine 
clas tics, sevc ral hundred metres thick, characte ri sed by 
glauconitc-bcaring sancis tones with subord inate quanti ­
ties or conglome rate, tulTiti c sandstone, tuff, and c lay 
(TISLJAR & SIM UN IC, 1978; SIM UNIC ct aI. , 1990). 
The strati graphic position of these sedimentary rocks is 

Faculty o f Mi ning. Geology and Petroleu m Eng ineeri ng, Unive rsi ty 
o f Zagreb, Pieroll ijeva 6. IIR - IOOOO Zagreb, Crolilia. 

Lower Miocene ( from Egerian to Karpathian), dur ing 
which sedimentation creating barrie r sand bars predom ­
in at ed , occasionally interrupted by dacite-andes it e 
explos ive volcani sm. Thc volcanism began to cease by 
the end of this period , and a new transgression and tec­
tonic movements prevented deposition of c lastic sedi ­
menls, and increased carbo nate sedimentation (S IM U­
NrC ct aI. , 1990). 

The Mace lj-sandstones are of homogcnous mineral 
composition with vari ation expressed through grain size 
and re lati ve pe rcent ages of vol cani c las ti c mate rial , 
matrix and ce ment. The de trital composition indicates 
sou rce arcas composed mostly of sedimentary rocks and 
schists. In the tulTitic sandstones the dis tinction between 
resedimentcd and directl y depos it ed volcaniclastic 
mate ri a l is ambiguous due to inte ns ive chloriti za ti o n 
and glauconitization. 'The matrix composition and tex­

ture seem to indicale direc t deposit ion of volcanic ash, 
which was produccd by periodic e ruplions in thc adja­
cent areas (TISLJAR & SIMUNIC, 1978). 

Th is pape r represents introdu c to ry work in the 
in ves ti ga tion of glauconitic mate ria ls of the Macelj ­
sandstones and the ana lys is of these matcrial s from 
three typical sandstone samples. Sample M3 was taken 
from the outc rop (l owe r part of the Lowe r Miocene 
mass ive Macelj-sandstones) on the Durmanec-Macelj 
road , ncar the borde r be twcen Croatia and Sloveni a (the 
border cross ing Maee tj). Sample RG was obtained from 
a drill core (at 31.5 m depth) from an exploratory we ll 
s ituated south-wes t o f the village of Strupari , soulh o f 
Mt. Ravna Gora. Samp le MT was take n from an o ut­
crop (uppe r part of the Lower Mioce ne c ross- bedded 
Macelj -sandslones) on the road ncar Donji Mace lj. The 
sample locations areyresellte? on ri g. I. 

Analogous to SRODON 's ( l 984) definition for 
ill it ic materials, in th is paper we used the te rm glau­
conitic Ilwte rial to refe r to both g lauconite and to inte r­
stratifi ed glauconite-s mectite, as we ll as to the ir mi x­
ture. 

2. DESCRIPTION AND MINERAL COMPO­
SITIONS OF SANDSTONE SAMPLES 

Th e sa mples of the Macelj~sands t ones wc re a na~ 

lysed by polariz ing microscope and X- ray powder dif­
fraction (XRO). 



18 

LEGEND: 

StrohinlCica Mt. 

., Mocelj sandstones" 
(LOWER MfOCENE) 

Sample M3 is a glauconitic sandstone com posed of 

poo rl y sorted , mos tly angular, rarely subrounded finc­

grai ned Lo medium -grained particles (0.3-0.7 mm in 
size). T he det ritus consis ts mostly of rock fragme nts 

with subordinate undu lato ry quart z, and very rare 

fe ldspars. The most comlllon accessory mine ral is gar­
ne t which is accompan ied by subordinate lOurmaiinc, 

apatite , muscov it e, biot it e and limonite aggrega tes . A 

green ish g lauconiti c mat ri x is predominant, together 
with dense chlorite-seric ite aggregates, which are prob­

ably a diagenet ic product of clays ri ch in organic impu­

ri ties. Caleite ceme nt occurs sporadicall y in intergranu­

lar pores. Rock fragment s are mostl y grai ns of 

quartzite , chert , c rystalline sch is ts, and occas ionally 
m<lcrocrystallinc dolomite. The undulatory ex tinction or 

q uartz grains indi cates it s me tam orphi c orig in. 

Fe ldspars are almos t completely seric itized ; rare relict 
grains d isplay zoning or dense polysynthe tic twinning 

and corroded edges. Fragments of extrusive rocks, with 

plagioclase phenocrysts and micas produced by dcvitri­
fi ca tion of volca nic glass were al so iden tifi ed. Some 

fi ssures in the detri ta l grains are s lightly greenish. 
Glauconitic mate ria l occurs in two basic form s : as 

de trital grains and as the matrix (Fig. 2a). Less com­

mon ly, thc dc trita l g lauconi tic material occurs as well 
rounded g rains composed of c ryptocrys ta lline "grape 

like" darkgreen aggregates . Most of the g lau conit ic 
matrix mate rial fills intergranular pores, is much 

brighter in colour and occurs as cryptocrysta ll ine, platy­
shaped aggrega tes, with s ingle minute se ricite and chlo­

rit e plates within the g lauconi ti c mate ria l. The g lau­

conit ic matri x is not evenly dis tributed throughout the 
rock, but is rather concentrated in the shape of laminae 
and inte rl aye rs w ith in the sandstone. Ofte n the re are 

laye rs composed nearly e ntirely of glauconitic matrix 
and interlayers in whi ch the glaucon iti c mate rial is 
a lmost absent. The glauconi tic mat rix di splays features 

of plastic defofmation and compact squeezi ng (e .g. 

sand grains which are nea rly complete ly wrapped in 
glauconitic material). 

Tu ff 
(LOWER MIOCENE) 

Geologi .. Cro~tic :l , Oil 

Fig. 1 Location map (modified from 
SiMUNiC el a\.. 1990). 

Sample RG is very s imi lar to sample M 3, partic u­

larly in the compos ition o f de trital grains , whi ch are 
better sor ted, subrounded to rounded , wi th s ize charac­
teri st ics of medium-grained to coarse-grained sand. 

The glauconitic mate rial occup ies inLe rg ranular 
pores in the pans that are c las t or matrix supported. In 
contrast to samples M3 and MT, there is no glauconitic 
materia l in the form of detrital gra ins. The g lauconiti c 
mate rial occurs in the matrix and it is most probably a 

produc t of glaucon itization of fin e volcanic ash Of 
glass. Thc glauconitic materia l displays feat ures of sed­
imcntati o n under semipi astic condit ions. T extura ll y, 

three types of the grccn glauconiti c matri x can bc d is­
tingui shed: darkgreen grapy aggregates (Fi g. 2b), ye l­
lowgreen, mo re or less homogeneolls c ryptoc rystalline 

aggregates, with weak pl eoc hro ism and with sparse 
mica, and fibrou s gree n agg regates with s trong 

pleochroism which are probably produced by g laLiconi­
ii zation of c hl o rite (Fi g . 2b). [n Ihc RG sands io ne, 

a ltered gra ins are preselll in which cryptoc rys ta lline 
quart z domina tes and whi ch are s lightly green along 
fi ssures (Fig. 2b) . 

Sample MT is a cross- laminated nne-g rain ed to 
medium-grained sandstone, wi th mai nly angular to sub­

rounded grains, rare ly with rounded grains, averaging 
0.1 -0.4 mm in size. The sandstone is composed of s ili ­
c ic las tic gra ins, glauconit ic mate ri al and matr ix w it h 
sporadi c calc ite cem ent. In contrast to the prev iously 

descri bed samples, silicic lasts of MT sandstone consis t 
of angula r to subangu lar quartz fragments mainly with 
undulat ory extinction. C las ts of quartzi te, che rt and 
low-me tamorphic to med ium -me tamorphi c g rade 
schis ts (quartz-sch ists) are common, wh ile to a lesser 
ex tent fragme nts of gneiss, mica-schis t, dolom itc, si lt­
stone and sodic plagioclase are also present. 1n thi s 
sampl e, det rital f1akes of muscovi te are quite frequently 
observed. 

Glauconitic material occurs mainly in the intc rgran­
lIlar pores of si Jiciclas ts as cryptoc rysta ll ine matri x or 

as mic rocrysta lline, platy ye llow-oli ve-green aggregates 



Tadcj, Slovcncc, Tisljar & Inkret: Glauconitic Materials from Lower Miocene .Vl:Jcelj-Sandstones ... 19 

c 
Fig. 2 a) Dark green grape-like detrilie glauconitic material and light green glauconitic matrix filling intergranular pores. Thin section of sample 

M3; I N, photo length 1.36 mm. b) Glauconitic matrix in the form of dark-green grape-like clusters and green fibrOllS clusters. Light green 
glauconitic material coatings in quartz rractures arc also present. Thin section of sample RG: IN, photo length O.S6 mm. c) Laminae with 
glauconitic matrix. Thin section of sample MT: I N, photo length 1.36 rum. d) Detritic grape-like dark-green glauconitic grain . Thin section 
of sample MT; I N, photo length 0.86 mm. 

(Fig. 2c). The structurc and rc lationship of the glau­
conitic material with these siliciclasts indicates that the 
ground mass was originally composed of fine volcanic 
ash or semilithified glassy tuff. The glauconitic mass 
frequently contains fine-dispersed pyrite and organic 
matter. The glauconitic matcrial matrix is commonly 
concentrated within single laminae. Glauconitic materi­
al rarely occurs in the form of spherical and grape- like 
grains (Fig. 2d), which can be distingu ished from the 
glauconitic matrix due to their more in tense green 
colour, and the lack of any internal microtexture except 
cryptocrystalline and microcrystalline aggregates. 

Despite some small differences, all the examined 
sandstones (M3, RG and MT) according to PETTI­
JOHN et al. (1972) can be classified as lithic graywack­
cs. 

XRD analysis, carried out 011 bulk-rock samples, 
shows that quartz is the dominant mincral in sample 
M3, which also contains a considerable amount of cal­
cite, subordinate plagioclase and K-feldspar, two chem­
ically different types of dolomite, and minor quantities 
of muscovite and siderite. The amount of glauconitic 
material is very small. The mineral composition of sam­
pic RG diffcrs from the M3 sample since it contains 

several times the amount of glauconitic material and 
considerably less calcite. SampieRG also contains two 
different dolomite types, some more plagioclase, a little 
chlorite, muscovite, and no siderite. Thc highest content 
of quart z and muscovite arc prescnt in sample MT 
which also contains dolomite and some calcite, plagio­
clase, K-feldspar, chlorite and haematite. The content 
or glauconitic material is higher in sample MT than in 
samplc M3. 

3, SEPARATION OF PURE GLAUCONITIC 
MATERIAL AND EXPERIMENTAL METHODS 

XRD patterns of the analysed bulk-rock sandstones 
samples could not be used to idcntify the glauconitic 
material due to the relatively small amounts prcscnt in 
th e sam pl es. Separation of pure glauconitic material 
was carried OUI, 10 enable further determ inatio n to be 
undertaken. 

After fragmentation, sievi ng and water washing, the 
0.1 -0.2 ml11 and 0.2-0.315 111m fractions were enriched 
in glauconitic material. These were later magnetically 
separated by a Frantz isodynamic separator. The mag-



20 

netic glauconitic fractions were obtained at I = 0.40-
0.55 A (labelled MT/l , M3/l and RG/l) and at I = 
0.55-0.60 A (labelled M3/2 and RG/2), and were finally 
purified by hand-picking under the binocular micro­
scope. Other magnetic fractions of analysed samples 
contained more impurities consist ing of other sandstone 
mineral constituents mixed with glauconitic material. 
After a purity check using XRD, small quantities of 
carbonate (dolomite, siderite, calcite) and amorphous 
Fc-compositions were removed from the M3/2, RO/2, 
M3/1 and MT fractions with d iluted hydrochloric acid. 
A method to obtain pure glauconitic material from pul­
verised glauconitic material fractions (aftcr separation 
in a Frantz isodynamic separator) using sedimentation 
from a water suspension was tested. The fraction < 111m 
was separated. The purity of glauconitic material from 
sample M3/2 obtained by this method was much higher 
than that obtai ned by hand-picking. The glauconit ic 
material obtained in this way was used in further analy­
sis. Olhcr samples purified using the same mcthod gave 
fractions of equal or less purity than the fractions 
obtained by hand-picking. 

Fractions M3/1 and M3/2 are equally distributed in 
scparated glauconitic material of M3 sample. In the 
M3/1 fraction the grains are mainly subrounded to 
rounded in shape. In the RG sample about 4/5 of the 
total glauconitic material content is in the fraction RO/l 
and about 1/5 in the fraction RG/2. In the MT sample 
almost all of separated glauconitic material is in the 

N 

" 0 

0 ~-
0 

~ 0 

I Ei- 0 

Ii:: ~ :; 
~- N ,- MT 
0 

A 
M3/1 

JL M3/2 

A 
RG/l 

A 
RG/2 

~ 
~ 

30 20 15 10 5 

8/°CuK" 

Fig. 3 XRD powder pallerns of separated g lauconite samples. The 
indices of diffraction lines of glauconitic material are indicated in 
lhe pattern of sampl e MT. C = chlorite; M = muscovi te: A = 
amphibole; Q = quartz: P = plagioclase. 

Geologia Croatica 5011 

MT/l, so only this fraction was analysed as represent­
ing sample MT. 

Depending on the increasing of magnetism the 
colour of the glauconitic material fraction ranges from 
light to very dark green. The M3 and MT glauconitic 
materials have a prominent blue shade whereas the RO 
fractions have a grass green colour, particularly when 
pulverised. 

Separated pure or nearly pure glauconitic material 
fractions (samples MT, M3/1, M3/2, RG/I and RG/2) 
were analysed chem ically, thermally and by XRD. 

XRD powder investigations were done on a Philips 
diffractometer, using CuKa radiation, a graphite 
monocromator and proportional counter. Diffraction 
pal terns of randomly oriented air dried samples, and 
specimens with prefe red orientation (air dried samples 
and samples treated by ethylene glycol) were recorded. 

Comparing glauconite/smectite and illite/smectite 
interlayered minerals VELDE & ODIN (1975) conclud­
ed that "illite and glauconite mixed layered phases 
appear to be crystallographically similar." Therefore we 
used the method for ident ification of illitic material by 
SRODON (1984) and SRODON & EBERL (1984) to 
identify the glaucon itic material in this study. 
SRODON (1984) used this mcthod for the identification 
of one glauconite sample (sample No 39 in table 2 of 
cited paper), too. According to them the ratio for pure 
illite is determined as follows: 

Ir = 
1(001)/1(003) (a ir dried sample) = 1. 

1(001 )/1(003) (glycolated sample) 

If the illitic material is expandable Ir will increase, 
i.e. the ratio increases with increasing amounts of the 
expandable component. With regard to layer intcrstrati­
fication , the glauconite-smectite series is similar to the 
illite-smectite series. For th is reason the Ir ratio has 
been used in this paper for comparison of glauconitic 
materials. 

The chemical analysis of separated glauconitic 
material was performed by classical chemical mel hods, 
while sodium and potassium were determined using a 
flam e photometer. Cation exchange capacity (CEC) 
was determined according to KjeJdahl (cit. SUS­
TERCIC, 1969) with previous replaccment of excha­
ngeable cations using ammonium acetate. 

Thermal analyses (DTA, TG, DTG) were performed 
by the MOM derivatograph, Budapest, with a heating 
rate of cca 10°C/min. To decrease the influence of rela­
tive moi slure contents, samples were stored in the des­
iccator for 24 hours before analysis. The weight of each 
sample used in the individual thermal analysis was 0.23 
g. The weight loss clue to dehydration was read from 
TG curvcs according to SCHULTZ (I969). 

4. RESULTS 

XRD powder patterns of randomly oriented ancl ori­
ented separated glauconitic material are shown in Figs. 



Tadcj. Slovcncc. l'isljar & lnkret: Glauconitic Materials from [,ower Miocene M<lcelj-Sandstolles ... 21 

15 10 

N 

"" "" 

1x 103 cps 

6/°Cu K« 
5 

MT(AO) 

MT(EG) 

M3/1 (AD) 

M3/1(EG) 

M3/2(AO) 

M3/2(EG) 

RG/H AD) 

RG/2(AO) 

Fig.4 XR D powdcr pa!lerns of oricnted samples. AD - air dried sam­
pic: EG - ct hylcnc glycol trcatcd sampl e: i'.,.l = muscovite; C = 

chlorite. 

3 and 4, which illustrate tha t samples MT, M3/1, M3/2 
and RG/l contain practically no impurities. In contrast, 
sample RG/2 conta ins numerous im puri ties (chlorite, 
muscovite, amphibole, quartz, and plagioclase). The 
same impurities are present in the < 1 !-un fraction of 

the RG/2 sample, indicating a c lose relationsh ip of 
glauconitic material and initial substrate of g lauconiti­
za tio n. Diffract ion patterns also show that this sample 
contains the highest quantity of expanding layers. 

Results of chemica l analysis and crystallochemical 
formula calculated on the basis of Olo(OH)l are present­
ed in Table 1. 

The Ir-values are presented in Table 2. 
Thennoanalyticai curves of separated glauconitic 

material s are shown in Fig. 5. The DTA curves display 
three endothermic effects; the first in the temperature 
interval from lOOoe to 200°C which correspond s to 
dehydration; the second in temperature interval from 
450°C to 600°C which corresponds to dehyd roxylisa­
tion, and the third, a weak effect at ~ 900 0 e which indi­
cates di sintegration of structure. According to UTSAL 
& UTSAL ( 1981) a weak exothermic effect at 360-
380°C may be indicative of the oxidization of structural 
Fe2

+. However, this effect is more obviously expressed 
in weakly magnetic frac tions, although their FeO con­
tents do not di ffe r essentially in wcakly and strong ly 
magnetic fractions of the relevant samples. For thi s rca­
son it is more probable that the exotherm ic effects men­
tioned above, indicate the presence of impurities that 
are not detected by XRD. 

Dehydration and dehydroxy li zat ion endothermic 
effects are accompanied by an eq uival ent weight loss 
on TO curves. Besides thc TO cu rves the lotal weight 
losses are also marked in Fi g. 5. The weight losses 
re latcd to ad sorbed and st ru ctural water, whi ch were 
de termined according to SCHULTZ (1969), arc pre­
sented in Table 2. 

S. DISCUSSION 

The AlPEA Nomenclature Committee (BAILEY et 
aI., 1979; BAILEY, 1980) have defined glauconit e as 
an Fe-rich dioctah edral mica with tetrahedral AI (or 
Fe3;.) greater than 0.2 atoms pCI' formul a unit and octa­
hedral R 3+ correspondingly greater than 1.2 atoms. The 
interplanar spacing d(060 ) is > I. S I ok Addi tional 
characteristics of glauconite are that the octahed ral 
charge is greater than +5.3 pCI' form ula unit and that the 
interlayer charge in non-expandablc spcc im ens varies 
from ~ +0.8 to +0.9 (BAILEY et aI. , 1984). According 
to the AIPEA Nomenclature Committee the species 
glauconite is a single-phase and, ideally, is not intc r­
stratified. Specimens with expandable layers can be 
described as randomly interstratified glaucon it e-smec­
tite. BUCKLEY et al. (1978) proposed that the term 
"glauconite" should be used only for those minerals 
cOl1laining less tl1an 5% intcrl ayering. According to the 
samc authors glauconites have mainly the IMd typc of 
structure as indicated by extended basal and reduced 
hkl reflections 011 thei r XRD powder patterns. StruclUr­
al imperfcctions of glau conites have previously been 
attribu ted to in terstralification. The heterogeneity in the 
composition and structurc of glauconite pell e ts was 



22 Geologia Croalica 50/1 

MT M3/1 M3/2 RG/1 RG/2 

Si02 51 .74 52.14 51.57 50.58 52.94 

Ti02 0.10 0.15 0.21 0.16 0.26 

AI20 3 6.14 11.42 16.44 9.33 10.94 

Fe20 3 18.98 13.03 8.60 18.46 15.84 

FeO 4.24 2.17 2.68 2.57 1.97 

MgO 3.23 5.17 2.07 3.45 2.21 

CaO 0.38 0.62 0.59 0.80 1.39 

Na20 0.29 0.35 0.55 0.41 0.40 

Kp 8.35 7.81 6.27 7.28 4.88 

H20
105 1.51 2.24 5.01 2.90 5.21 

LOI 5.20 4.85 6.24 4.63 4.45 

Total 100.1 6 99.96 100.23 100.57 100.49 

Si 3.79 3.70 3.71 

AI 0.21 0.30 0.29 

AI 0.32 0.66 1.11 
Fe3+ 1.05 0.70 0.47 
Fe2+ 0.26 0.13 0.16 

Mg 0.35 0.55 0.22 

Ti 0.01 0.01 0.01 

Ca 0.03 0.05 0.05 

Na 0.04 0.05 0.08 

K 0.78 0.71 0.58 

L (R"R") 1.99 2.05 1.97 

L R" 1.37 1.36 1.58 

LA 0.85 0.81 0.71 

used to explain the existence of a series from 1M to 
IMd type structu re (BURST, 1958; I-lOWER, 1961 ; 
BENTOR & KASTNER , 1965). However, SAKHA­
ROY et a l. (1990) demonstrated that homogenous glau­
conites without expandable layers can also give weak 

and broad Ilk! reflections due to thc presencc of struc­

tu ra l dcfects resulting from variolls types of 2:1 layer 
stacking faults. For this reason, the amount of expand­

ing layers must be also determined in glauconite sam­

ples. Numerous authors determined that as the K and 
Fe3+ conte nts dec rease, the amount of Al vl increases 

together with the number of expandable layers 

(ODOM,1984). 

3.66 3.80 

0.34 0.20 

0.46 0.72 

1.01 0.85 

0.16 0.12 

0.37 0.24 

0.01 0.01 

0.06 0.11 

0.06 0.06 

0.67 0.45 

2.01 1.94 

1.47 1.57 

0.79 0.62 Table I Chemica l analyses and the num-
ber of ions pCI' 0lo(OH)2" 

In the present study the proportions of expandable 
layers (Table 2) have been estimated using the CEC 
values (MANGHANI & HOWER, 1964) and the K 
content (THOMPSON & HOWER, 1975) and by com­
pari son of XRD patterns of glycol-solvated samples 

with computer calculated diffraction profiles given by 
THOMPSON & HOWER (1975) . The est imated pro­
portions of expandable layers are also fairly compatible 

with the co ntents of adsorbed water and the If-values 

(Table 2). 
For all samples studied in this paper Ir > I (Table 

2). According to the method of SRODON (1984) and 
SRODON & EBERL (1984) the plotted 002 and 003 

Weight losses I % 

Percentage of expandable layers CEC Kions Ir according TG curves 
from from K from mEq/100g per adsorbed structural 

Sample CEC' contenf XRD2 O,,(OH), water water 

MT 0 5 5 7.1 0.78 1.40 1.42 4.68 

M3/1 5 >5 5 10.2 0.71 1.61 2.16 4.62 

M3/2 12 10-15 10 15.6 0.58 1.93 3.79 4.62 

RG/1 < 10 < 10 <10 12.1 0.67 1.87 2.82 4.34 

RG/2 35-40 nd 40 31.5 0.45 nd 5.09 4.23 

Table 2 The contents of expandable layers and corresponding pararnetars for their estimation. Legend: I according MANGHANI & HOWER 
( 1964); 2 according THOMPSON & HOWER (1975): nd - not determ ined. 



Tadej. Slol'cllec. Tisljar 8.: Ill l-rel: Glauconitic tvtucrials from Lowcr Miocene Milcclj-S:lIld~toncs ... 2J 

MT 
M311 

M3/2 

RG/1 

RG/2 

MT 
M3/1 

M3/2 

RG/1 
RGI2 

100 11){) 300 

DTA curves 

TG curves 

6.10 

6.78 

8.41 

7.16 

9.32 

~oo 500 600 700 1100 900 I/"C 

Fig. 5 Thermoanalyticul Curves of glauconite silll1ples. Weight loss 
Cll rves include corrections from blank curve (althe bollom of fig­
ure). Percenl weight losses arc indicated along TG curvcs. 

re fl ex posi tions of g lyco lated samples re ll in the illit e 
riel d or velY close 10 it (rig. 2 in SRODON, 1984). No 

samples plotted in the illite/smectite ( liS) field. There­

fo re, acco rdin g to SRODON (1984) and SRODON & 
EBERL (1 984) all analysed samples (except RG/2) pre­
sent the same type 01" illitic ( in our paper glauconi tic) 
materia l: mixtures 01" pure illite (respec tively glauco­

nite) and an ISH-ordered mineral with < 15% S. 

1.6 

I.' 

1.2 

M3/2 
1.0 . 

~0.8 

0.6 

0.' 

0.2 

0.0 +----.-,----,---.---,..----'>,.-,-"--,r­
o 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 

Fe]" 

Fig. 6 Trivalent octahedral ion contents (RJ
') per formu la unit. Solid 

lines indicate li mits or glauconi te R) ' content (mod iried from 
BUCKLEY cl aI., 19X4). 

In rclation to K content , the MT sample is practical­
ly no n-interstratified. Sample M3/2 contain s more 
smec tite layers according to the K con tent and CEC 
value (Ta ble 2). It has higher expandability than sug­
gested by the res ult s of SRODON (1984) and 
SRODON & EBERL ( 1984) method. 

Sa mple MT contai ns only a few ex pandable layers 
(Table 2) and its structural chemica l rOfl11uia is very 
close to the avcragc formula of unaltered glauconites 
analysed by BUCKLEY et a1. (1978). This is confirmed 
al so by its plot on Ihe Alv1-Fe" di agram (Fi g. 6) , as 
wcll as its position on the diagram which di splays the 
re lation of d(060) spacings to Fe'" ions (Fig. 7). The 
XRD pattern (Pig. 3) indicates a IMd type s truc ture; 
however, among all samples analysed in the present 
study, the MT sample has the less reduced ilkl re fl cc­
tions. All these parameters indicate that the MT sample 
in fact almost represents single-phase glauconite. 

Samples M3/1 and M3/2 have IMd structure (Fig. 
3). Sample M3/1 conlains a little bit more than 5%, and 
sampl e M3/2 contains 10% to 15% smectiti c layers 
(Table 2). Accordi ng to THOMPSON & I-lOW ER 
( 1975) both samples show "IMIl" type or o rdering. The 
relationsh ip bctween thc number of octahedral AI J 

.. and 
FcJ 

.. ions for both samples corresponds to glauconite. 
Samp le M3/2 plot s ve ry ncar to the boundary of the 
glauconite fi cld (Fig. 6). The high Alv, content or both 
samples gives rise to the small d(060) values: 1.5 11 A 
(M3/l ) ancl 1.510 II (M3/2) . These values are very 
close to the celadonite-glaueonite boundary as proposed 
by BUCKLEY ct al. ( 1978), but on the Fe)· vs. d(060) 
diagram, both samplcs plol withi n the glauconite fi e ld 
(Fig. 7). 

Due to the sma ll amo unt 01" expandable layers in 
sample M3/l, the average chemi ca l co mposition 01" 
non-ex pandable layers in it is not essentially dirl"erent 
from the bu lk chemical composi tion presented in Table 
1. It was not possible to determ ine the average chemical 
composition of non-expandable layers in sample M3/2, 
but due to very hi gh Al vr content in the bulk sample 
(Table I), il probably corresponds 10 AI-glauconile. 

1.51~O 

1.5110 
0< 
~ 1.5150 

~ 1.5IJO 

1.5 110 

1.5090 M3/2 

++MT 
RG/1 

+RG/2 
+ M3/1 

L-~~ __ ~ __ ~ __ ~_ 
0.4 0.6 1.0 1.2 

Fi g. 7 Relationship of d(060) spacing 10 Fe)' ions. Solid lines indi­
cate approximatc limits of glauconitc (modified from BUCKLEY 
et al. , 19R4). 



24 

Samples M3/l and M3/2 per formula unit con tain 
0.66 and 1.11 AI" atoms and 0.55 and 0.22 Mg atoms, 
respective ly (Table I ). The large differences in the 
octahed ral atom content between the two fractions of 
sample M3 cannot be explai ned either by d ifferences in 
the amount of expanding layers (l>= 10%), or by differ­
ences in the degree of maturity of glauconite. This dif­
ference in chemical composition indicates e ither differ­
ent initial substrat es of glaucon iti zation, or different 
ellv ironments of glauconitization. Microscopic data ancl 
dilTcrcnccs in the shape and colour or separated grains 
suggest that detrital glauconitic material is predom inant 
in the M3/1 fraction whereas the matrix glauconit ic 
material is predominant in fraction M3/2. 

RG samp les have essentially different XRD pat­
terns (Figs. 3 and 4). The RG/ I sample has IMd type of 
s tructure and co ntains < 10 % expandable layers, and 
according to THOMPSON & HOWER (1975) s hows 
an "IMII" type or orde ring. In the octahedral AI 3+_Fc3+ 

ion diagram (Fig. 6) ancl in the d(060)-Fch diagram 
(Fig. 7), the sample plots in the glauconite fie ld very 
close to sample MT. 

The glaucon ite component in thc RO/2 sample eOIl­
tains 35-40% expandable layers and, according to 
'T'HOMPSON & I-[OWER ( 1975), represents randomly 
interstratified glauconite-smectite. Chemical compari ­
son between samp les RG/l and RG/2 is not poss ible 
bec~\L1se sample RO/2 contains impurities and therefore, 
the chemical com position of smectite is unknown. 
However, on the basis of opt ical analysis it is presumed 
that glauconi tic matcrial from samplc RG/ L (predomi­
nant ly in the form of dark-grcen grapy aggregates) and 
RG/2 (probably other types of glauconitic matri x) rep­
resent different phases of an evolved glauconi te scrics 
originated from samc or similar initial substrate of glau­
con iti zation. Microscopic observations (Fig. 2b) and the 
mincra l composi tion determined by XRD (Fig. 3) sug­
gcst th at the g laucon itic material from the RO/2 is a 
product, at leas t partly, of ch lorite and probably mus­
covite glauconiti za tion . 

In concordance with ODIN & MATTER ( 1981) and 
ODIN & FULLAGAR (1988) we identify these stages 
of g lauconitization for analysed "glauconitic minerals": 
evolved to highly evolved (MT and M3/l), evolved 
(RG/ I), s lightly evolved to evolved (M3/2) and sl ightly 
evolved (RG/2). 

6. CONCLUSIONS 

The Macelj-sandstones were deposited in shallow­
marine environ ment s on forcshores , shorefaces, and 
tidal flats with or without deltas at stream and small riv­
er mouths . The detrit us load for thc marine shoal s, 

Geologia Croarica 5011 

which were often separated from the open sea by sandy 

bars and tidal fla ts, is debris transported by rivers from 
areas of act ive erosion. Periodic but explosive synsedi­
mcntary dac ite-andesite volcanism made possible tuff 
accumulation (for example, in the area of Donje Jese­
nje) and the presence of great quantit ies of volcano­
c lastic matcrial within the epiclastie detritus. The vol­
caniclastic material in the detritus was deposited cithcr 

direct ly during volcanic eruptions, or by it s re-deposi­
tion and acc umulation with the de tritus of the Macelj ­
sandstones. 

Data obtained from analysis of 3 samples of the 

Macelj-sandstones show that there arc differences not 
only among glauconitic material from various locat ions 
but also among glauconit ic matc rial from the same 
sandstone sample. These dilTerences are already notice­
able from the microscopic examinatio n of sandstones 
and after glaucon ite separation. 1n the strong ly magne­
tic fractions the glauconitic material has a darker grcen 

colour than the weakly magnetic fraction and, based on 
analytical data, thc fomlcr is more evolved. ]n the scrics 
from highly cvolved to less evolved glauconi tic materi­

a ls, the proportions of expandi ng layers increase from 
< 5% to approximately 40%. 

Heterogeneity of the M3 sandstone re late s to the 
magnetic features of glaucon it ic mate rial and the pres­
ence of dctrital glauconitic grai ns po int to redeposition 
during glauconi tizat ion. Significant dilTercnces between 

the chemical composi tion of samples M3/ 1 and M3/2, 
part icu larly in AI, Fe and Mg proportions, may suggest 
differences in the initia l subst rate of glaucon itiza tion 
from sample M3 as well as differences in comparison 
wi th glauconitic material from sa mples RG andMT. 
The de tected mineralogical differences betwcen g lau­
conit ic matcria l from sample M3 are cons istent wi th the 

microscopic data which indi cates redepos ition of an 
unconsolidated scdiment. Chemical differences of mag­

netically morc homogeneous glauconi tic matcria l from 
sands tone RG may be expla ined by differcnces in 
chem ical and stru ctu ral features within the evolving 
series of glaucon ites which or igi nated in the same glau­
coni ti za tion cycle, from probably the same or si milar 
initial substrate. In the MT sample only one single mag­
netic frac tion was obtained and thus it can be presumed 
that the subst rate of glauconitization was unifo rm in 
composi tion. 

The results obtained from th is invesli ga tion ne ither 
deny nor confirm the rcsu lts achieved by other investi­
gators (T[SLJAR & SIMUNIC, 1978; S IMUN IC et aI., 
1990), indicating that glauconitic material from the 
examined Macclj-sandstones were probably produced 
by alteration of dacite-andesite volcano-clast ic material 
in shallow-marine environments. 



Tadej. Slovcncc. Tislj;Ir & Inkrct: Glauconilic Maleri;l!.'> from Lower Miocene Macclj-SandslOIlCf' ... 25 

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BA ILEY , S.W., BRINDLEY, G.W., KODAMA, H. & 
MARTIN, R.T. (1979): Report of the Clay Minerals 
Society Nomenclature Committee for 1977 and 
1978.- Clays Clay Miner., 27,238-239. 

BENTOR, Y.K. & KASTNER, M. (1965): Notes on the 
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spccies.- Mineral. Mag., 42, 373-382. 

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BURST, J.F. ( 1958): Mineral hClerogcncity in "glau_ 

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GORJANOV IC-KRAMBERGER, D. ( 1904): Gcologi­
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and origin of glauconite.- Amcr. MineraL, 46, 313-

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Amer. Mineral., 49, 586-598. 

ODIN, G.S. & f'ULLAGAR , P.O. (1988): Geological 
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Ncw York-Heidelberg-Berlin, 615 p. 

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SCHULTZ, L.G. ( 1969) : Lithium and potassiulll 
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SRODON, 1. (1984): X-ray powder diffraction identifi ­
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Manuscript received May 19, 1995. 
Revised manuscript accepted April 28, 1997. 



26 Geologia Croatica 50/1