Journal of Minerals & Materials Characterization & Engineering, Vol. 6, No.1, pp 53-67, 2007 Printed in the USA. All rights reserved
Characterization of Opaques off Konkan Coast
Maharashtra, Central West Coast of India
Gujar, A.R 1., Angusamy, N2, and Rajamanickam, G. V.3
1 National Institute of Oceanography, Dona Paula, Goa, India – 403 004.
2 Dept. of Earth Sciences, Tamil University, Thanjavur, India – 613 005. Email:
3 Disaster Management, SASTRA Deemed University, Thanjavur, India – 613 402.
Characterisation of opaques, comprising of ilmenites and magnetites,
separated from the sediment samples off Konkan coast, has been attempted. On the
basis of dominance of intergrowth of the exsolved or replaced phases, magnetites of
Vijayudurg and Wada vetye are grouped together while the magnetites of Ambolgarh
and Rajapur are showing similar characteristics. Ilmenites display intergrowths with
hematite and rutile. In Ambolgarh and Rajapur, ilmenites of exsolved and replacement
phases are abundant with alterations along the borders. On the basis of intergrown
lamellae width, the source rock for the ilmenites is attributed to the distant
metamorphic rocks
The presence of altered ilmenites testify a higher percentage of TiO2 in
Ambolgarh and Rajapur. A higher amount of FeO (35.79 % - 36.25 %) in Wada Vetye
and Vijaydurg is ascribed to higher percentage of ilmenite – hematite phase in the
exsolved ilmenites. REE pattern of ilmenites, magnetites and non-magnetics show an
enrichment of LREE over HREE. Ilmenite, magnetite and non-magnetics show a
negative Eu anomaly which is ascribed to the individual or combination of the
following conditions: 1) Melt effect, 2) Crystallo-Chemical effect, and 3) Competing
mineral effect. A higher enrichment of TiO2 in the ilmenites reflects the possibility of
establishing down-stream industries as well as the suitability for converting ilmenites
into synthetic rutile.
Key Words : Opaques, Intergrowth, REE, India.
The world reserves of economic sources of titanium are estimated to be
approximately 300 million tons that contained TiO2 [1]. Major resources occur in
54 A.R. Gujar, N. Angusamy, and G.V. Rajamanikam Vol.6, No.1
Australia, Canada, China, India, New Zealand, Norway, South Africa, Ukraine, and
the United States. World production figures of titanium minerals indicate that 55 %
production is made available from shoreline deposits and the rest 45 % from the
magmatic source (Force, 1980). The demand for ilmenite is driven, to a large extent,
by growth in demand for TiO2 pigments. TiO2 pigment is mainly used in the Paints &
Coatings (59 %), Plastics (20 %) and Paper (13 %) industries [2].
Trends such as use of bright glossy finishes in paints, higher demand for light
paper, increased paper recycling, and substitution of traditional materials with plastics,
on substantial scale, correlate to a growing demand for TiO2 pigment in these
application areas. Of the total global inferred reserves of 1418 million tones of
titanium minerals, India has a reserve of about 348 million tones [3]. However, when
the production of ilmenite is looked into, the ratio of production of ilmenite to the
reserves is only 0.1 % while the countries such as Malaysia (7 %), USA (3 %),
Australia (1 %) and Brazil (1.8 %) keep better ratio [1].
India is blessed with large reserves of strategic and economically important
heavy minerals such as leucoxene, zircon, monazite, ilmenite, rutile, garnet and
sillimanite. In India, a two stage model for pseudo-rutile formation from the ilmenites
of Manavalakurichi region has been reported [4] and the alteration of ilmenites from
the river Valliyar and Manavalakurichi beach has been outlined [5]. Along the
Ratnagiri coast, the provenance of offshore ilmenite placers, based on geochemical
studies has been dealt in detail [6,7]. From South India, a detailed account of alteration
characteristics of ilmenites has been enunciated [8]. However, characterization of
opaque minerals is not yet attempted from the present study region. The present work
highlights the distribution pattern of intergrowths of opaque minerals viz., ilmenite
and magnetite and their chemical compositions for exploitation.
From the Konkan coast, only four southern bays viz; Wada Vetye, Ambolgarh,
Rajapur and Vijaydurg have been taken up for the present study. These bays with
Wada Vetye in the North, and Vijaydurg in the South (Fig.1) are bounded by
submergent type of coastline, which is very irregular and indented. W adavetye b ay is a
straight and promontories in the North and South.
The Ambolgarh bay is gentle, arcuate to semi arcuate in shape. The Rajapur
bay has small pocket bay behind the promontory, whereas the Vijaydurg has an
arcuate bay (Table 1). The Ambolgarh bay is a protected zone and does not have any
river or stream source.
A van Veen grab (0.04 m2 scoop area) was used for the collection of surface
sediment sample (116 Nos) from the near shore region of the Konkan coast (up to 20
m water depth). Samples were washed and dried. After coning and quartering,
carbonates, organic matter and ferruginous coatings were removed from the samples
Vol.6, No.1 Characterization of Opaques 55
Table 1: Characteristics features of the bays
Bays vijayadurg Rajapur Ambolgarh WadaVetye
Shape Arcuate Arcuate Arcuate to
semiarcuate Staright
configuration NNE-SSW E-W NE-SW N-S
Promotionaries N & S N & S S S
Beach Sandy sandy Sandy Bouldery and
coarse sand
Wind Partially
protected Partially
protected Protected Open condition
Lnadforms Sandbar-
Mudflats and
Sandy beachTombolo Bouldery beach
56 A.R. Gujar, N. Angusamy, and G.V. Rajamanikam Vol.6, No.1
by treatment with 1:10 HCl, 30 % by volume H2O2 and SnCl2, respectively. The dry
samples were sieved at Ro-Tap sieve shaker for 15 minutes. Heavy mineral separation
was carried out by using a bromoform of 2.89 specific gravity [9].
Ilmenites were removed using the Cook isodynamic separator, having the
forward slope of 15o and a side tilt of 10o at 0.2 Amp. The separation was confirmed
by X-ray diffraction on a Philips PWG. 1840 Powder diffractometer. Representative
detrital ilmenites (8 Nos) and magnetites ( 8 Nos), covering the bays, were mounted
on a bakelite medium and after polishing, under reflected light, examined for their
nature of intergrowths and exsolution structure, etc. Chemical analysis of
representative ilmenite (8 Nos) and magnetite (8 Nos) was done by preparing single
solution [10,11] using GBC – UV Visible Spectrophotometer. Ferrous oxide
determination was done by titration method [12]. Trace and REE analyses (ilmenite 8
Nos, Magnetite 8 Nos and Non-magnetics – 2 Nos) were carried out in ICP – Mass
Spectrometer [13].
Under microscope, magnetites of Wada Vetye bay shows almost an equi-
distribution of magnetite + hematite and magnetite + ilmenite ( Fig.2 A). In addition,
magnetites show exsolution texture with hematite (Fig.3 A), ilmenite or ulvo-spinel,
hematite or sphene and rutile. Titano-magnetites are criss-crossed by exsolved rutile
needles (Fig.3 B).
Ambolgarh bay is marked by the domination of pure magnetite (Fig. 2 A).
However, irregular grains are marked by the development of martites along the
border (Fig.3 C). Titanomagnetites with ilmenite and martites along the borders are
also noticeable (Fig. 3 D). Magnetites with exsolution and replacement textures and
sphene are insignificant. In Rajapur, again pure unexsolved magnetites with
maghemeite, are dominant (Fig. 3 E). However, magnetites, intergrown with hematite,
prevail over magnetite + ulvo-spinel + hematite and rutile, higher than other bays
(Fig. 3 F, G, H, I, J, and K). Broadly, Vijaydurg and Wada vetye can be grouped
together while Ambolgarh and Rajapur can be clustered together (Fig.2 A).
Ilmenite shows intergrowth textures with hematite and rutile (Fig.3 L). Among
them, seriate type of intergrowth is preponderant in Ambolgarh and Rajapur bays. In
the seriate texture, the thickness of exsolved ilmenite or hematite is not uniform, since
the exsolution bodies grow by diffusion. In few ilmenites, broad lamellae of hematite
are alternately arranged parallel to each other without the intercalation of other phases.
Large grains of ilmenite show lamellar twinning including rutile needles along (0001)
and (0011) planes (Fig. 3 M). Ilmenite grains are also characterized by alteration along
the boundaries.
In Ambolgarh, ilmenites are subrounded, showing dominant replacement
texture by secondary hematite and rutile (Fig.2 B). These forms are free from any
coatings. Besides, exsolution with hematite and rutile, it is replaced along the border
Vol.6, No.1 Characterization of Opaques 57
by sphene (Fig.3 N). In the exsolved phase, width of the hematites fluctuates 25 - 32
Rajapur bay is dominantly made up of pure ilmenites with alterations along the
boundaries, ilmenite + hematite and ilmenite + rutile (Fig.2 B). Ilmenite grains are
irregular in shape and form. Exsolution intergrowths with lamellae of hematite are
arranged along (0001), (0111) and (0112) planes of the host. The width of the hematite
lamellae ranges 20 - 36 µm.
Vijaydurgh bay is consisting of ilmenite, ilmenite + rutile and ilmenite +
hematite. Grains are sub-angular to sub-rounded in shape, showing exsolution with
hematite and also replacement of ilmenite or ilmenite/hematite exsolution by sphene
(Fig.3 O, P). The width of the hematite lamellae in the exsolved ilmenite of this bay
varies 29 - 38 µm.
The width of the intergrown hematite lamellae of ilmneites derived from
igneous rocks ranges up to 80 µm whereas the width of 20 – 40 µm is attributed to
metamorphic rocks [1]. In the present study region, even though basaltic rocks are
exposed adjoining the coast, the presence of fine lamellae (20 – 35 µm) in the
exsolved hematite phase points to the source, probably from metamorphic rocks
rather than from hinterland basaltic rocks.
The purity of separated ilmenite concentrates has also been confirmed by X-
ray diffraction where ilmenites with different inter-planar intensity spacings are
clearly demarcated. In addition, the intergrowths of ilmenites with rutile are confirmed
at 27.1 to 27.6o, as ilmeno-rutile (Fig.4). Magnetites are also characterized by well
developed secondary digitations at 100 % peak, clearly indicating the exsolved phase
of magnetite with hematite, rutile and ulvo-spinel (Fig. 5 ).
The opaque minerals, comprised of ilmenite and magnetite, do indicate the
differential distribution in magnetite fractions, comprising magnetite, titanomagnetite
and their intergrowths. Rajapur bay is distinguished from the rest in having higher
pure magnetites. Ambolgarh, though adjacent to Rajapur, establishes a difference by
higher titano-magnetite. Vijaydurg and Wada Vetye bays display a similar
characteristics of magnetite and titanomagnetite. In the case of ilmenite, all the bays
are noticed to have more or less uniform trend but for minor variations in their
association with sphene, magnetite and rutile (Fig. 2 B).
58 A.R. Gujar, N. Angusamy, and G.V. Rajamanikam Vol.6, No.1
Vol.6, No.1 Characterization of Opaques 59
a. Exsolution of hematite with titano-magnetite in lamellar pattern
and replacement of hematite along cleavage plane (Wada Vetye)
b. The exsolved magnetites with hematites
c. Irregular magnetite grains with martitisation along the border
(Ambolgarh bay)
d. Titano-magnetite with ilmenite and white coloured martite along the
border. Another titanomagnetite is also seen on the right (Ambolgarh
e. Grain of pure magnetite with maghemite (Rajapur bay)
f. Intergrowth of ilmenite+magnetite with hematite. Replacement of
hematite is also seen (Vijaydurg bay)
g. Graphic texture formed by magnetite with hematite (Vijaydurg bay)
h. Magnetite with hematite and alos whitest part of martite in the centre
of the grain
60 A.R. Gujar, N. Angusamy, and G.V. Rajamanikam Vol.6, No.1
I. Seriate texture with alternate bands of hematite exsolved in
magnetite. (Vijaydurg bay).
j. Replacement of magnetite along the borders by sphene and hematite
patches (Vijaydurg bay)
k.Magnetite with inclusions of sphene and white streaks of hematite
(Vijaydurg bay)
l.Ilmenite-magnetite grain with rutile needles and replacement texture
of hematite along the cleaveages (Wada Vetye bay)
m.Rutilated ilmenite (Ambolgarh bay)
n. Ilmenite showing complete replacement by ilmenite-hematite phase
by sphene (Vijaydurg bay)
o. Exsolved ilmenite with hematite and replacement of hematite along
the rhombohedral edge (Vijaydurg bay)
p. Ilmenite replaced by hematite along the cleavages producing cloth
Vol.6, No.1 Characterization of Opaques 61
Ilmenite composition indicates a TiO2 variation from 38.41 % to 45.20 %
(Table 2). Broadly, the chemical analysis has shown a close similarity among
Ambolgarh and Rajapur bays’ ilmenites whereas ilmenites of Vijaydurg and Wada
Vete follow a similar pattern. Ambolgarh and Rajapur ilmenites register a lower Ni,
Zn and Cu, P2O5, CaO, MgO and FeO but higher TiO2 (43.57 % - 45.80 %). The
distribution of these elements along with Fe and Mg clearly attests to the nature of
higher unexsolved ilmenites, ilmenite + rutile. In Wada Vetye and Vijaydurg bay, a
negative correlation is established by TiO2 with FeO (r = -0.77), Cr (r = -0.60).
Successive stages of alteration of ilmenite have been attributed for the depletion of
FeO [1]. The presence of altered ilmenites in Ambolgarh and Rajapur testify a higher
percentage of TiO2 . A higher amount of FeO (35.79 % - 36.26 %) in Wada Vetye and
Vijaydurg is ascribable to higher presence of ilmenite – hematite exsolved phases.
Chemical analysis of magnetite indicates a distribution of Fe2O3 in Wada
Vetye (Av. 58.25 %), Ambolgarh (Av. 54.33 %), Rajapur (54.60 %) and Vijaydurg
(54.43 %) (Table 3). A higher percentage at Wada Vetye and lower concentration at
Vijaydurg, with almost equi-distribution in Ambolgarh and Rajapur can be earmarked
to nature of magnetite intergrowth. While Wada Vetye displays more magnetite +
hematite + ilmenite, Vijaydurg is dominated by pure magnetite. TiO2 deteriorates in
the descending order from Rajapur, Vijaydurg, Wada Vetye to Ambolgarh. This can
be ascribed to the differential replacement of mangnetite with rutile, ilmenite and
Chondrite normalized REE pattern [14] of ilmenite shows enrichment of LREE
(Table 4) over HREE (Fig. 6). The pattern shows increase in the elements according to
the increasing atomic radius, suggesting that the LREE have undergone fractionation
from HREE. A comparison with ilmenites of Manvalakurichi, India, where it is being
commercially exploited [15] shows that ilmenite in the study area is rich in LREE as
well as HREE. REE pattern of the ilmenites of the study area shows a negative Eu
anomaly which could have been resulted due to any one of the following conditions
either together or independently, i) melt effect, 2) crystallo-chemical effect, and iii)
competing mineral effect [16].
The chondrite normalized REE pattern of magnetite shows that there is a well defined
enrichment of LREE concentration (54.62 – 60.56 ppm) over the HREE
concentrations (11.50 – 12.18 ppm). The ratio varies LREE/HREE from 4.74 to 4.94
(Av. 4.85). The profile (Fig.6) shows a distinct – Eu and Ce anomalies and the order
of enrichment of the REE increases in the elements of increasing atomic radius. The
enrichment of LREE in the magnetites could have been resulted due to the preferential
incorporation of LREE relative to HREE formed during partial melting [16],
62 A.R. Gujar, N. Angusamy, and G.V. Rajamanikam Vol.6, No.1
Table 2:- chemical composition of representative ilmenite from the study area
WadaVetye Ambolgarh Rajapur Vijaydurg
V-105 V-81 Av. A-60 A-30 Av. R-15 VD-64 VD-15 VD-39 Av.
SiO2 0.35 3.63 3.56 2.17 3.6 2.71 2.87 4.45 2.17 1.8 2.8
Al2O3 1.37 2.24 1.3 0.98 1.52 1.25 0.88 1.2 1.05 0.23 0.82
TiO2 40.39 35.54 38.41 43.95 43.32 43.57 45.85 30.72 46.6 43.2 40.17
Fe2O3 14.26 18.22 16.24 16.82 12.65 17.73 16.96 18.96 15.6 14 16.18
FeO 35.92 36.61 36.26 31.65 29.52 30.58 30.55 38.9 30.95 37.52 35.79
MnO 0.43 0.41 0.42 0.43 0.34 0.38 0.41 0.29 0.37 0.77 0.47
MgO 2.04 1.87 1.95 1.66 1.15 1.4 0.66 2.71 1.04 0.82 1.52
CaO 0.46 0.32 0.39 0.16 0.36 0.26 0.19 0.64 0.78 0.62 0.68
P2O5 0.18 0.26 0.22 0.19 0.11 0.15 0.2 0.24 0.31 0.23 0.26
V2O5 0.02 0.02 0.02 0.02 0.02 0.01 0.02 0.03 0.16 0.02 0.06
Table 3:- chemical composition of representative magnetite from the study area
WadaVetye Ambolgarh Rajapur Vijaydurg
V-105 V-81 Av. A-60 A-30 Av. R-15 VD-64 VD-15 VD-39 Av.
SiO2 3.28 0.3 1.79 0.8 0.2 0.5 0.12 3.18 1.1 1.2 1.82
Al2O3 5.2 1.4 3.3 2.91 0.45 1.68 0.84 3.32 3.8 2.01 2.9
TiO2 12.45 17.96 15.21 15.3 14.62 14.96 16.78 13.36 16.05 16.74 15.38
Fe2O3 56.5 60.2 58.25 52.5 56.16 54.33 54.6 51 52.69 53.61 52.43
FeO 18.07 15.92 16.99 23.16 22.33 22.74 23.4 24 20.43 22.4 7 22.3
MnO 0.32 0.46 0.16 0.44 0.4 1 0.42 048 0.42 0.49 0.51 0.46
MgO 1.28 1.8 1.29 2.99 3.27 3.12 2.85 1.51 1.25 1.48 1.41
CaO 0.74 0.64 0.68 0.84 0.71 0.75 0.52 0.71 0.72 0.63 0.68
P2O5 0.21 0.36 0.28 0.4 0.48 0.44 0.28 0.55 0.41 0.18 0.38
V2O5 0.2 0.04 0.22 0.04 0.03 0.03 0.04 0.03 0.22 0.04 0.06
Vol.6, No.1 Characterization of Opaques 63
which further indicate that the incorporation of lanthanides in the magnetite is
not based on reduction in ionic radii. The observed Eu anomaly, in magnetites as well
as in the non-magnetics, can be due to the prevalence of low pressure crystallization of
plagioclase feldspar prior to magnetite crystallization from the melt [17]. This
anomaly could be generated, due to the preferential uptake of Eu by other phases,
crystallizing simultaneously along with magnetite (Complex mineral effect). The Ce
anomaly implies conversion of Ce4 + to Ce3 + at the time of fractionation.
Titanium dioxide is by far the most important and intermediate product of the
world titanium industry. The whiteness of titanium oxide and light scattering effect
makes it as the only suitable pigment for paint, paper and rubber industries. Fine
grained ilmenites can be used as a constituent of anti-corrosive paints as a substitution
for graphite. Minimum purity for ilmenite is mineralogically 98 % homogenous and
chemically, it should contain 40-58 % of titanium oxide. Enrichment of TiO2 in the
ilmenites of the present study region, shows a close correlation with ilmenites of
Canada, USA and Brazil where it is currently under exploitation. A higher
concentration of TiO2and FeO reveals that the ilmenites of the present study region
can be exploited for application in paint industries.
Table 4 chemical analysis of REE and trace elements of the representative
ilmenite, magnetite and Non-magnetites (values in ppm)
1 2 3 4 5 6
La 18.36 19.7214.9413.4717.2730.58
Ce 27.54 26.5626.0923.7730.0952.89
Pr 4.12 4.43 3.16 2.73 3.86 5.68
Nd 16.82 16.1314.3812.4816.7827.27
Sm 2.22 2.43 1.99 2.17 2.99 4.38
Eu 0.65 0.53 0.65 0.38 0.88 0.8
Gd 2.44 2.3 1.78 2.07 2.9 4.38
Tb 0.52 0.43 0.55 0.41 0.62 0.83
Dy 3.3 2.61 2.31 2.53 4.22 5.61
Ho 0.81 0.72 0.67 0.56 1.07 1.46
Er 3.25 2.68 2.13 1.8 3.35 5.56
Tm 0.72 0.76 0.39 0.45 0.5 0.95
Yb 5.72 5.34 3.17 2.73 4.58 6.86
Lu 1.05 1.05 0.52 0.57 0.77 1.42
64 A.R. Gujar, N. Angusamy, and G.V. Rajamanikam Vol.6, No.1
Trace elements
Sc 71 69 45 45 44 61
V 129.09 1600 1989 2222 1167 1351
Cr 210 249 266 331 268 267
Co 121 123 134 139 82 102
Ni 139 139 207 210 111 129
Cu 354 314 718 886 815 809
Zn 152 179 376 421 133 146
Rb 2 1 3 2 3 2
Sr 22 23 39 28 126 47
Y 14 14 13 13 23 34
Zr 3264 3111 1744 1607 1862 3455
Nb 327 3 181 175 156 266
Ba 25 35.6730 29 25 30
Hf 56 30 31 28 31 57
Ta 11 1 7 6 5 10
Pb 15 19 12 15 11 15
Th 12 15 7 7 10 21
U 1 1 1 2 2 4
1 & 2-Ilmenite (Wadavetye & Vijaydurg)
3 & 4 – Magnetite (Wadavetye & Vijaydurg)
5 & 6 – non-magnetite (Wadavetye & Vijaydurg)
Characterisation of opaques, consisting mainly of magneites and ilmenties,
under microscope shows the presence of both exsolved and replacement textures. In
Ambolgarh and Rajapur, ilmenites of exsolved and replacement phases are abundant
with alterations along the borders. Fine lamellae of exsolved hematite phase in the
ilmenites of the studied region, points out the possibility of its derivation from
metamorphic rocks, rather than from the exposed basaltic rocks. Ilmenite composition
indicates a TiO2 variation from 38.41 % to 45.20 %. Altered ilmenites account for
higher percentage of TiO2 in Ambolgarh and Rajapur. REE studies show –ve Eu
anomaly in the ilmenites, magnetites and non-magnetics, which could have been
caused by melt effect, crystallo-chemical effect and competing mineral effect in the
melt. Enrichment of TiO2 brings out that ilmenites can be exploited for converting
them into synthetic rutile by sulphate processes.
The authors are thankful to Dr.Satish Shetye, Director, NIO, Goa for providing
permission to publish this work. This paper has NIO’s contribution number.
Vol.6, No.1 Characterization of Opaques 65
66 A.R. Gujar, N. Angusamy, and G.V. Rajamanikam Vol.6, No.1
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