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3.2.4. Rock utilities

Rock utilities

Humans have always used rocks as a raw material to make their tools, build their homes, make their jewelry and ornaments, and more recently, as a source of energy.

Currently, mining associated with rocks is still very important, since rocks are essential in many economic sectors.

Rocks are of interest for their physicochemical properties (hardness, impermeability, etc.), as a source of energy or for the chemical elements they contain.

Rocks, according to their usefulness, can be classified into these groups:

Rocks of industrial interest

Rocks of industrial interest are rocks that, due to their properties, are used for the construction of houses and public works: conglomerates, gravel and sand as aggregates (crushed rocks) to make concretelimestone and clay to make cement, clay to make products ceramics (bricks, tiles, etc.), slatesquartz to make glass, etc.

Some of the main materials used in construction come from rocks:

  • Cement. Formed from the firing of ground limestone and clay. By adding water to this mixture, it hardens after drying.
  • Concrete. If sand and gravel are added to the cement, concrete is obtained, which is stronger than cement.
  • Ceramics. It is created from water modeled clay and fired at high temperatures.
  • Glass. It is obtained from a mixture of silica with potash or molten soda.

Phosphate rocks and evaporites are also used to make explosives, paints, fertilizers, and pharmaceuticals.

It should also be noted in this section the importance of the industrial minerals that the rocks contain and that contain very important and necessary chemical elements, such as iron, copper, lead, aluminum, etc.

Las rocas son de gran interés para la construcción de edificios y obras públicas

Is glass the same as crystal?

Although you surely use them as synonyms in colloquial language, glass and crystal are not the same.

It was already commented when we saw the definition of mineral , that it was a crystal when its components were ordered, and a glass, if they were disordered.

Surely this will not have made it entirely clear to you, but don't worry, the RAE will not either.

Glass: Brittle and transparent or translucent hard material, without crystalline structure, obtained from the fusion of siliceous sand with potash and moldable at high temperatures.


Glass: Glass, especially high-quality glass.


The main difference between glass and crystal is in their structure. The crystal is formed by a regular atomic structure, perfectly ordered. The structure of glass, on the other hand, is irregular. The same raw materials, depending on how they are cooled, will give rise to a crystal or a glass.

Although in everyday language we can use both terms as synonyms, in geology class we must use them correctly. The term crystal will be used to talk about a mineral, of natural origin, created without the intervention of the human being, such as a quartz or fluorite crystal, for example. In addition, objects such as glasses, cups, plates, etc., which have lead oxide in their composition, are also made of glass. The presence of lead in the composition facilitates cutting and engraving. It also makes it denser and refracts more light. The glass used to make figures has up to 49% lead to make it more malleable and shiny. A glass exposed to sunlight refracts the light showing a range of colors like the rainbow.

The windows, the glasses, the "good" cups are made of glass.

A simple trick to recognize if a glass is glass or crystal is to listen to the sound that is produced when hitting it with a finger. If the sound in a dull "pec" it will be glass, but if it is a long "piiing", the cup will be glass. In addition, crystal glasses, due to their lead content, will be heavier, more transparent, thinner and more delicate.

Another difference between glass and crystal, resulting from the manufacturing process, is that heat-treated glass is safer, as when it breaks it breaks into small, non-cutting pieces. Ordinary glass and crystal, on the other hand, would produce dangerous sharp pieces.

Glass can be recycled and reused without losing quality, so it is very important that we deposit it in the green container. Glass, on the other hand, cannot be recycled, since the lead in its composition means that it has a much higher melting temperature than glass and cannot be melted in the same ovens. For this reason, we will throw the glass into the gray (or green) container, but not the glass container.

Game: Do you know in which container you have to throw each waste?.

Rocks as sources of energy

Coal and oil (which we have already seen is a rock) are used as a source of energy, since combustion produces a lot of energy.

Although the main use of oil is its use as fuel, it must also be taken into account that other products are obtained from oil, such as plastics, paints, fertilizers, tar, etc.