Glass with a high lead content

Glass with a high lead content is used in the nuclear industry, because it has better X-ray and gamma radiation retention than normal glass.

A mineral is a compound or single substance, which occurs as a solids in the wild and is formed by geological processes. The science that studies minerals is called mineralogy; mineralogy has interfaces with chemistry: both scientific disciplines investigate the composition of minerals.

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Minerals are often recognised in the field by their crystalline form, their colour, their stripe colour (the colour they give off when scratched), their hardness, their melting behaviour, their association with other minerals, and so on.

This classic macroscopic form of recognition requires a lot of experience and is not always reliable. In geology, therefore, more and more reliance has been placed on retrospective analysis of optical properties other than colour, especially through polarisation microscopy (light microscopy with polarised light), X-ray powder diffraction, X-ray fluorescence spectrometry, electron beam microanalysis (electron microprobe) and atomic absorption spectrometry. In some cases, infrared analysis is applied.

A rock or the mutual claws of a rock consist of one or more minerals or mineraloids. These determine the properties of the rock: the colour, the hardness, how easily the rock wears off, etc. Mineraloids are inorganic natural materials that do not have an ordered chemical structure, such as opal or chalcedony. Minerals are all solid, inorganic natural materials that have an ordered chemical structure, a crystal lattice. The most common minerals are called rock-forming minerals. Examples of rock-forming minerals are quartz, calcite, feldspar, amphiboles, mica’s, pyroxenes and olivine. Most rocks consist for more than 90% of at most three or four of these minerals. Usually, small amounts of other minerals are also present.

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Each mineral has its own unique chemical composition and internal structure, with which the atoms are arranged within the crystal lattice. The crystal lattice determines the shape and fission of the crystals that make up the mineral. In some crystal lattices the atoms are closer together than in others, these minerals are denser. Minerals with the same chemical composition are called polymorphs. Diamond, for example, is a polymorph of graphite, both minerals consist of pure carbon, but diamond has a denser crystal structure. Under high pressure, graphite can convert to diamond, such a transition from one polymorphic to another is called a phase transition.

Chemical composition
Which minerals are present in a rock depends in the first place on the chemical composition of the rock. A rock that contains enough silica (SiO2, the oxide of the element silicon) may contain quartz or another mineral consisting of pure silica. The rock-forming minerals consist almost exclusively of nine elements (silicon, sodium, potassium, aluminium, oxygen, hydrogen, iron, magnesium and calcium). Together, these elements make up 98% of the total mass of the continental earth’s crust.

Most rocks consist mainly of silicates, minerals that contain silica. Almost all coagulation rocks and most sedimentary and metamorphic rocks are included. An important exception is carbonate rock, which consists of carbonates (compounds of carbonate, CO32-). Examples of carbonate rocks are limestone, marble and dolostone. There are other exceptions, such as halite (rock salt) and gypsum are also not silicates.

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This breccy is an example of a clastical rock in which the cliffs (dark) of the matrix can be clearly distinguished. Because the cliffs all consist of the same limestone, the distinction is sharp. Location: slope of the Devínska Kobyla in the Slovakian Small Carpathians. Age: Early Jurassic.
Two rocks with the same chemical composition do not have to contain the same minerals. Whether a certain mineral could be formed in a rock depends on the temperature and pressure that prevailed in the rock and the composition of any liquids that flowed through the rock.

Texture
Some rocks consist exclusively of minerals, the crystals of which have grown together, they are crystalline substances. However, there are also rocks that consist of fragments of minerals or dead organisms. Such fragments are called claws and these rocks are called clastic rocks. Examples are sand (and sandstone), clay, conglomerate or breccy. Some clastic rocks consist of very different claws: pieces of different types of rocks or minerals, fragments of shells, plant remains or fossils.