Minerals

In general, minerals have a crystalline structure. Therefore, minerals are also crystals. A crystal is a solid substance whose atoms or molecules are arranged symmetrically, which results in symmetry of the external form. When minerals are bound by more or less flat surfaces that can be admired with the naked eye, we speak of crystals. There are, of course, exceptions to this rule, that is, there exist minerals that do not have a crystal structure. They are called amorphous minerals. Notable examples include opal and obsidian, a type of volcanic glass, as well as mineraloids such as copal and amber. Up to today, more than 4,000 different naturally occurring minerals have been identified. Each of them has a unique crystal structure which is determined by the arrangement of elements in the crystal lattice and by their chemical composition.

Crystals are formed in natural environments through crystallisation processes. The vast majority of these processes are hidden from view, occurring deep below the Earth’s surface, or are very slow. This makes them difficult to study. Crystallisation in solutions or melts begins with the formation of crystallisation seeds or crystallization nuclei. Once a nucleus forms, the crystal begins to grow around it in such a way that the elements of the basic cell of the crystal are repeated in all three directions of space. Formation of a crystal depends on several factors, such as the presence of chemical elements, appropriate temperature and pressure, space, time, as well as the pH and Eh of the environment. Depending on the chemical composition and crystal structure, minerals and the rocks they are made of display different properties.

Our ancestors soon realised that some minerals can be very beautiful. In Slovenia and across the world, many archaeological artifacts were found that bear witness to the fact that minerals and precious rocks have always been very popular, admired and valued as aesthetic objects. This is the precious world of gems. Even today, jewels are used as expressions of personal, emotional and sensual worth and are generally understood as symbols of wealth and power. Natural stone has always been the noblest, but also the most durable natural material, which has been confirmed again and again by archaeological finds. Many works of art also make use of natural stone. Gems were used for aesthetic purposes by artists and noble stones served as building material for countless craftsmen across time and space.

 

Rocks

Earth is a living, dynamic planet. Unlike the Moon, our Earth is an ever-changing World. We can observe how some rocks are formed, for example during volcanic eruptions, or how they are destroyed by weathering and how they transform under erosion. The main drive for the circular flow of rocks on Earth is hidden deep inside our planet. If you were to cut through the Earth, you would see a layered structure composed of a core, a mantle and a crust. The core was formed very early after the birth of our planet, when heavier metallic, mainly iron-nickel minerals were separated from silicate minerals, which remain in the mantle and the crust.

Processes inside Earth and on its surface cause the continuous formation and reformation of rocks, which circulate in the so-called rock cycle. As the magma cools beneath the surface of the Earth, intrusive rocks are formed. Meanwhile, the surrounding rocks change into contact metamorphic rocks as a result of increased temperature. In a process that is called convection currents, magma from the Earth’s depths rises towards the surface through areas of rifting, which causes the continental crust to break up. Here, submarine springs of basaltic lava create new oceanic crust. Molten magma also flows to the surface through volcanic hotspots, which form the volcanoes of volcanic island chains, and through volcanoes above subduction zones, where oceanic plates subduct under continental plates. Along these subduction zones, upon the collision of two continental plates, high mountains are formed. By transportation, sedimentation and solidification of their weathered remains, clastic sedimentary rocks are formed. Sediments can also be produced as a result of chemical precipitation or by the excretion of marine organisms (coral reefs, etc.). In cases where tectonic plates collide and transport sedimentary rocks to lower layers of the Earth, they are transformed under the influence of increased pressure and temperature into metamorphic rocks. If they sink even deeper into the Earth’s interior, they melt again and form a new generation of igneous rocks. In rare cases, a special type of volcano can eject extrusive rocks mixed with diamonds to the Earth’s surface. Finally, space rocks are brought to Earth by meteorite falls.