4311) About Minerals And Rocks, Croatia: Metamorphic rocks, Igneous rocks, Sulphur - Radoboj, Hrvatsko zagorje, Serpentinite - Roknić strana, Bović, Banovina: Date/Year of Stamps issue: 21.01.2026:
The science that explores the formation and classification of rocks is called petrology. Rocks build the lithosphere, a rocky layerthat encompasses the Earth's crust and the upper part of the Earth's mantle.
In terms of their origin, rocks are classified as igneous, sedimentary and metamorphic. Igneous rocks are formed by crystallisation or solidification of magma in the interior of the Earth or lava on the surface of the Earth.
Sedimentary rocks are created on the surface of the Earth by sedimentation of material formed by the wear of already existing rocks by the action of water, wind or ice, or by sedimentation of residues of organisms, or by chemical sedimentation from supersaturated solutions.
Metamorphic rocks are
formed by transformation of already existing rocks, whether igneous,
sedimentary or even older metamorphic rocks, during which the recrystallisation
of minerals occurs in a solid state due to the influence of temperature,
pressure and fluids.
Igneous rocks
make up about 95% of the lithosphere, whereas the other two types of rock are
only 5% of the lithosphere.
Rocks are aggregates of one or more minerals, and a mineral is a natural solid formed by geological processes, with a specific chemical composition and crystal structure, stable under certain temperature and pressure conditions. Minerals are made up of atoms interconnected by different types of chemical bonds that are regularly repeated in space, forming a crystal lattice.
Minerals can occur as crystals -
as a homogeneous, regular geometric solid with some degree of symmetry, which
is a reflection of their regular internal composition, but they occur even more
often in nature as different aggregates. All known minerals are divided into
classes according to their chemical composition and structural characteristics
(I - native elements, II - sulfides, III - sulfosalts, IV - oxides and
hydroxides, V - halides, VI - carbonates, VII - nitrates, VIII - borates, IX -
phosphates, arsenates and vanadates, X - sulfates, XI - tungstates and
molybdates, XII - silicates and XIII - organic compounds) that are defined by a
dominant anion or an anion group.
Minerals that have the same dominant anion or
anion group have many similarities and often occur together in similar
geological environments. The scientific study of the chemical
composition, crystalline structure and physical properties of minerals, as well
as the study of the formation of minerals and their classification,
distribution and their use, is called mineralogy:
Sulphur - Radoboj, Hrvatsko zagorje
One of the oldest known chemical elements is sulphur, and when it appears in nature in its elemental form, it is a mineral from the class of native elements that belongs to the group of non-metals.
Native sulphur is most often formed near volcanic vents and fumaroles by sublimation from a stream of hot gases, and smaller quantities can be produced by the consumption of sulfide and sulfate minerals.
It crystallises in the orthorhombic system and often appears in the form of dipyramidal crystals, or as a massive and sometimes powdery aggregate.
Its colour is typically yellow, and it can also be yellow-brown, reddish, greenish to gray, while its streak is always white. On crystal surfaces, sulphur has a strong diamond shine, and at the fracture its shine is resinous or waxy.
Sulphur has an incomplete cleavage by three plane systems, and its fracture is conchoidal to irregular. It is of low hardness and relatively low density.
Sulphur is the tenth most abundant element in
the universe, where it is formed in the interior of massive stars by the fusion
of silicon and helium, while in the form of sulphides it
appears in many types of meteorites, especially ordinary and carbon chondrites.
On our planet Earth, sulphur is even more common, and as the fifth most common element, it appears either as an integral part of sulphide and sulphate minerals, or as a native element.
More than 1000 different types of minerals are known to contain sulphur in their composition, which is due to the ability of sulphur to form compounds with numerous other chemical elements.
In his book Specijalna mineralogija [Special Mineralogy] Fran Tućan states the following for sulphur:
“In Croatia, the most important site is in Radoboj near Krapina, where it is found in the Sarmatian marl... It developed in two layers. In the upper layer, which is composed of blackish flaky shale, ..., sulphur is scattered in clumps, which are as big as a walnut, an apple and a human head.
Beneath that layer lies a layer of sandy shale full of insect and plant fossils, and underneath it a layer with sulphur, which is mixed with gray shale matter.”
Sulphur was discovered in Radoboj at the beginning of the 19th century, which began the mining history of the region, and the exploitation of sulfur using the world-famous Radoboj machine lasted for more than a century.
Serpentinite - Roknić strana, Bović, Banovina:
Serpentinite is a rock that consists for the
most part of one or more minerals from the serpentine group - phyllosilicate
minerals that occur naturally as dense scaly or fibrous aggregates
formed by the low-temperature hydrothermal process of olivine or pyroxene
mineral exchange in primary ultrabasic rocks.
It is a metamorphic rock of green to dark green color, mesh or lattice texture that resembles snake skin, which is why it was named after the Latin word “serpens, (which means snake).
The process by which these changes in minerals occur is called serpentinization, and it takes place most often deep on the seabed on the borders of tectonic plates at temperatures from 200°C to approximately 500°C and under atypical chemical conditions with the presence of water as an oxidizing agent.
During serpentinisation, the rock absorbs large amounts of water, resulting in an increase in volume, a decrease in density and destruction of the original texture of the rock, and the release of gaseous hydrogen, which plays a significant role in the formation of methane and hydrogen sulphide, together with which it is the main source of energy for deep-sea chemotrophic microorganisms.
Serpentinites are very often an integral part
of ophiolite zones, rock masses that represent the remnants of the oceanic
crust and the upper part of the Earth's mantle, formed in the oceanic
environment near mid-ocean ridges, or subduction zones, and have reached land
by tectonic movements.
It is interesting to mention that the name ophiolite comes from the Greek words ophis and lithos, which mean snake and rock, respectively, due to the fact that it contains serpentinite.
In the Banovina area, serpentinites appear as parts of older metamorphic and ultramafic complexes that are associated with the remains of former oceanic lithospheric plates.
The area belongs to the Central Dinaric Ophiolite belt that stretches from Banovina through Bosnia and Herzegovina to Serbia and represents part of the ancient Neotethys Ocean that began to form about 250 million years ago by the separation of the supercontinent Pangaea into Laurasia and Gondwana.
That ancient ocean disappeared about 50 million years ago when the Indian tectonic plate collided with the Eurasian plate, creating the Himalayan mountain range.
The Postage stamps:
Technical details:
Issue Date: 21.01.2026
Designer: Dean
Roksandić, designer from Zagreb
Printer: AKD d.o.o., Zagreb
Process: Offset Printing
Colours: Multicolor (CMYK)
Size:
Stamp size:
29.82mm x 35.50mm,
Souvenir sheet size:
112.00mm x 73.00mm
Values:2.50 EUR (x 2
Stamps)
Links to Posts on Croatia on this Blog:
Castles of Croatia Stamp Series:
Santosh Khanna has commented:
ReplyDelete"A VERY informative post. Thanks for sharing."
Thank you so much Khanna sahab.
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