is a type of clay consisting predominantly of montmorillonite.
Bentonite’s mineral and chemical compositions vary
considerably with montmorillonite comprising typically between
40% to 65% together with variable amounts of illite, kaolinite,
aluminosilicates and minor amounts of gypsum, sodium chlorite
and calcium carbonate. The
bentonitic clays of Cyprus were deposited as deep-water
sediments from the alteration of volcanic ash during the Upper
Cretaceous period (approximately 90 million years ago), roughly
contemporaneously with the Upper Pillow Lavas or locally with
the umber and radiolarites of the Perapedhi Formation. They were
then either reworked or directly overlain by the pinkish clay
and chalk of the Lefkara Formation.
has a very high plasticity, good swelling properties and
variable colour from greenish grey/yellowish brown to khaki or
pinkish. The key
property of bentonite that makes it an industrial mineral with a
variety of uses is the ability to swell with absorption of water
and shrink with the expulsion of water.
The amount of water it can absorb reaches five times its
weight and is associated with an increase of its volume of up to
15 times. This
property can be repeated many times.
To be suitable for commercial exploitation the raw
bentonitic clay material should have the following properties:
low calcium carbonate, high montmorillonite content, low soluble
salts (chlorides and gypsum) and high plasticity.
Tests used on raw bentonite include moisture content,
Atterberg limit, swelling properties (absorption rate),
montmorillonite content, chemical analysis particularly for
carbonate content and water-soluble salts and water absorption.
is excavated periodically from shallow quarries and transported
to factories where it is laid down to dry and is blended before
processing. Most of
the bentonitic clays from Cyprus are exported for use as pet
litter. However, a sodium activation process has been developed to
improve the properties of the natural bentonite. The main uses of bentonite internationally include drilling
muds, foundry sand binders, civil engineering and iron ore
quantities of bentonitic clays are used in Cyprus for
geotechnical works such as dam construction.
Bentonite outcrops widely around the Troodos Mountains, covering an area of about 80 km2. Taking account of other geological constraints the total resource is estimated around 2 billion tonnes. The deposits vary considerably in size and in distribution but comprise more or less regular layers that may reach more than 50 m in total thickness. Some gypsiferous bentonite outcrops south of Arsos village in the Famagusta district with an estimated reserve of about 400,000 tonnes.