.................................................................... The minerals

Introduction. This chapter is dedicated to the study of mineral matter, which are the inert (non-living) materials that constitute the mountains, valleys, deserts, etc. In nature there are two types of mineral matter: rocks and minerals. The difference between them is that the minerals are the elements that constitute the rocks, which means that rocks are always made by two or more kinds of minerals. This is easily seen if you look at a piece of granite, like the one shown in the photo below. It can be noticed that it is not made by only on substance, but three. There are white-greyish, white and black particles.

  • The white-greyish particles are the mineral called "quartz".
  • The white particles are the mineral called "feldspar" and
  • " The black particles are the mineral called "mica biotite

Each of the observed particle is called mineral particle and each type of particle is called mineral species. The photo shows that there are many mineral particles but only three types of mineral particles: quartz, feldspar and mica biotite.

Activities to do. Read the explanation on the concept of minerals and the classification of them and do the "Multiple Choice Test 5". Then read the text on the properties of minerals and mineral deposits and do the exercises "Identification of minerals and their properties 5" also "Crossword 5".

1 . Mineral. A mineral is a natural, inorganic, solid, crystal matter with a fixed chemical composition or a composition that vary between very narrow limits.

1.1 What does natural mean? A substance is called natural when it is originated in nature, that is to say, without human intervention. The matter produced by humans is called artificial material. For example, cement and steel are not minerals, since not found in nature but they are products manufactured by humans.

1.2 What does inorganic mean? A natural substance is called inorganic when it does not constitute nor characterize organisms, in other words, when it is not made of carbon (C) and hydrogen (H) atoms. Those are the two essential elements that form the organic matter, which is the one that composes the organisms. An example of an inorganic material is sodium chloride (NaCl) and an examples of an organic matter are the lipids composed mainly with C and H.

1.3 What does a solid matter mean? A substance is called solid when the particles (atoms, molecules or ions) are tightly bound and occupying fixed positions. This means that a force must be used to deform or break it. Thus, for a substance to be considered as a mineral, it is necessary to be solid. The water is not a mineral, nor is the oxygen of the air, etc. The usual saying "mineral water" does not mean that the water is mineral but that it came from the inside of the mountain, that is from a mine of water.

1.4 What does crystal mean? A solid matter is called crystal when its particles are arranged, that means the particles are not placed in any shape, but in fixed locations, such that, if the sufficient space is available, they form geometric shapes such as cubes, prisms, pyramids, etc., which are called crystals. When the number of particles is big enough, the crystals are visible to the naked eye.

In exhibitions and trades of minerals, we often speak of "crystallized minerals" when crystals are visible to the naked eye, and "mineral mass" when they are not. Actually, the second ones are also mad of crystal matter. Only by observing them under a microscope we can appreciate its small microscopic crystals. When hard minerals are formed, they can be exploited to make a durable jewelry. Large crystals are very rare and that makes them highly prized. When solid particles are unordered they are said to be amorphous solid matter.

By the unit cell we call the crystal as small as possible, that is constituted by the minimum number of particles (atoms, molecules or ions). A crystal visible to the naked eye is not more than a repetition, sometimes an infinity and in the three dimensions of space, of the unit cell. .

1.5 What does having a defined chemical composition mean? The minerals have a chemically defined composition when the ratio of the chemical elements forming it is constant or has only minor variations. For example the galena ore has a sulfur atom per each atom of lead. It can also contain atoms of silver, gold and other elements, but without exceed 0.3% (called "impurities") if otherwise it is no longer called galena but a different mineral.

1.6 The fake minerals or mineral-look-alike. They are natural, inorganic and solid substances as limonite, opal and obsidian, that are not authentic minerals, because its particles are unordered, that is they are the amorphous matter. Also considered as mineral-look-alikes are inorganic liquids which can be found in nature, such as wate and native mercury.

 

2 . The classification of minerals. Scientifically, the minerals are classified according to their chemical composition, but this classification precise to have a knowledge of chemistry that are dealt with in the courses superior to this one. Therefore, the following is the classification of minerals according to its usefulness. In this classification, two large groups are differentiate:

2.1 The non-metallic minerals. They are not used to obtain metals. The principal are:

  • silicates (such as quartz, orthoclase feldspar, albite feldspar, biotite mica or black mica, muscovite mica or white mica and olivine),
  • carbonates (such as calcite and aragonite),
  • sulphates (as gypsum), and
  • salts (as halite and sylvite).

Most of those minerals are associated with other minerals to form rocks, and because of that they get the name of petrogeneric minerals. The principal are silicates, since they are the ones that make a majority in rocks forming the mountains (forms rocks such as granite, porphyry, basalt and clay). Then, there are carbonates, because the calcite is the main mineral in the limestone which also forms many mountains.

2.2 The metallic minerals. They are used to obtain metals. Usually they don't form rocks and can be found in small quantities, that is why is needed to use mines in order to reach them. When extracting, usually are attached to pieces of rocks. The metallic mineral that is extracted is called ore and the rock that accompanies is called bargain. Below is a table of the main minerals grouped by ore that is obtained from them. The diamond is also included, for being the most appreciated for their hardness beauty.

The metallic minerals and diamond.
(The names of the photographs minerals are shown in blue)
Iron minerals (Fe): Oligist, magnetite y siderite. The iron is used in the constructions of houses and in manufacturing machines.

Cooper minerals (Cu): Chalcopyrite, azurite, malachite, and native cooper. Cooper is used as a conductor of electricity, manufacture of boilers, pipes and coins; and exterior coating.

Lead minerals (Pb): Galena. Lead is used to manufacture pipes, as a protection for the radiation and to produce pigments for paints.

Zinc minerals (Zn): Blenda. Zinc is used to protect roofs and exterior doors; and to protect the iron (galvanized).

Aluminium minerals (Al): Bauxite. Aluminum is used to make cars, doors, windows and kitchen utensils.

Tin minerals (Sn): Cassiterite. Tin is used to protect iron (tin).

Mercury minerals (Hg): Cinbabar. Mercury is used for the manufacture of thermometers and barometers.

Sulfur minerals (S): Pyrite and native sulfur. Pyrite, given its high percentage of sulfur, does not work to get iron, only to produce sulfuric acid.

Gold minerals (Au): Native gold. Gold is used in jewelry and for making coins.

Silver minerals (Ag): Argentite and native silver. Silver is used in jewelry, coins and in photography.

Platinum minerals (Pt): Native platinum. Platinum is used in jewelry and to promote chemical reactions in industry.

Carbon minerals (C): Diamond. Given its hardness is used to make drills and cutting and polishing tools.

 

Multiple Choice Test 5. (Spanish activity. Activity in English is under construction)

3 . The properties of minerals. There are three types of properties: geometric, physical and chemical properties. Within these three, can be distinguish the following types:

Geometric   Symmetry
     
  Mechanic Hardness, Exfoliation and Tenacity
  Optic Color, Radius, Brightness and Refraction
Physical Electric Conductivity
  Magnetic Magnetic attraction
     
Chemical   Solubility and Effervescence with HCl

GEOMETRIC PROPERTIES. Are related to the shape of crystals. The most important is symmetry.

• Simetry. Symmetry is defined as the existence of an object oriented equally but in different directions. For example, a cube presents symmetry respect to an imaginary axis of rotation, passing through the center of one side and the center of the opposite face, since by rotating the cube relative to said imaginary axis, one of its faces repeats four times.

MECHANICAL PROPERTIES. Are the properties related to the application of force on the crystal. The main ones are hardness, toughness and exfoliation.

• Hardness. The hardness of a mineral is the resistance to being scratched. The more tightened the particles are, the harder it is. A mineral can be both hard and fragile, because although the bonds are strong if the structure has little stability, it can be broken easily. For example, the diamond, which is the hardest mineral that exists, is quite fragile.

In 1920, German mineralogist F. Mohs proposed a ladder of ten levels of hardness, in which each mineral radius is scratch by the one that lays in higher level. The Mohs ladder is:

        • Can be scratched by nail: 1 . Talc and 2 . Chalk
        • Can be scratched by razor: 3 . Calcite and 4 . Fluorite
        • Can be scratched by file: 5 . Apatite and 6 .*Ortosa
        • Can scratch glass: 7 . Quarz, 8 . Topaz, 9 . Corundum and 10 . Diamond
Gypsum (hardness 2) is cut with calcite (hardness 3)

• Exfoliation. Is the ability of some matters to break, resulting in flats. This is due to the existence of "binding forces between particles" which is differenced depending on the considered direction. Some minerals, when receiving hits, break into cubes, such as galena, other into slices, such as gypsum and micas, others into octahedrons, as fluorite, etc. The results, crystals, are called exfoliation solids. In the market of collectors, they are not as valued as natural forms. Specialists in cutting gemstones (gemologists), before deciding to work a piece, examine it carefully to deduce the possible cleavage planes. Non-exfoliation minerals when broken show uneven surfaces dominated by fractures. For example conchoidal fracture (in shape of shells) characteristic of quartz, splintery, scaly, etc.

The galena is exfoliated into cubes

Toughness. Is the resistance of a mineral to deform or break, which is the separation of its particles. According to this feature there are several types of minerals:

    • Elastic. When force is used, they recover to the primary shape.
    • Plastic. When force is used, they do not recover to the primary staying deformed.
    • Ductile. When stretch, yarns may result.
    • Malleable. When smashed, can get the shape of thin sheet.
    • Fragile. When force is applied, they break easily without getting a shape of plane sheet.
The mica crystals are elastic

OPTIC PROPERTIES. Are related to the behavior of light influencing the mineral. The main ones are color, stripe color, brightness and refraction.

Color. The color of a mineral is the kind of light that reflects when illuminated. It is one of the most efficient characteristics for identification. Some minerals may present different colors, depending on the type and amount of impurities they contain, resulting in the so-called "varieties". For example the mineral quartz, can occur in the varieties: pure quartz, also called hyaline quartz or crystal rock (which is colorless), smoky quartz (black), rose quartz (pink), amethyst (purple), citrine lemon yellow) etc.

Color of stripe or plain stripe. Is the color of the mineral powder. It is called stripe color because usually mineral dust is obtained by pressing the mineral against a plate porous of white porcelain and drawing a line on it, as if using a chalk on a blackboard. Depending on the color of the mineral stripe it can match its surface or be completely different. For example, pyrite is golden and the stripe is black. The color of the stripe is very useful for identifying minerals.

The pyrite is golden and the stripe is black

Brightness. The brightness of a mineral is a degree to which the light is reflected from its surface. There are brillant minerals and mate minerals. The most popular types of brightness are: metallic, vitreous, silky, pearly, adamantine, resinous and crass (greasy).

Refraction. Is the change of direction that is experienced by a beam of light while passing from one medium to another. The light, firstly passes from air to the mineral, and if it is transparent, then back to the air. In some minerals the light beam during the pass, split into two beams, leaving two images. This phenomenon is called birefringent. The transparent variety of calcite called Island spar, which is an example of birefringent mineral. The minerals which do not exhibit this behavior are called monorefringent, for example rock salt or halite are monorefringent minerals.

Island spar is a mineral birefringent

ELECRIC PROPERTIES. Are those that relate to electrical current. The best known is the conductivity, which is the ability to pass an electric current.

MAGNETIC PROPERTIES. Are those associated with magnetism, which is the ability to attract the iron. Some minerals like polar magnetite are able to attract small iron such as nails, tacks, etc. and deflect a compass needle. Others minerals present lower degree of magnetism, whereby its magnetism is only detectable when pulverized and by the magnet approaching to see whether it attract particles or not. .

Magnetite attracts iron clips

CHEMICAL PROPERTIES. Are those properties that depend on the ability of the mineral to react chemically with other substances. The most important are the solubility and the effervescence with hydrochloric acid.

The solubility in water. The soluble minerals can have taste and odor. For example halite is salty, slivina is salty and spicy, epsom salt is bitter, etc.

The effervescence with hydrochloric acid (HCl). The ability of a mineral to react with the acid by realizing bubbles and carbon dioxide (*CO2). This reaction is useful to identify the calcite ans aragonite, which are te basic minerals of limestone.

Calcite produces effervescence upon contact with hydrochloric acid

4 . The mineral deposits. The minerals deliver to humankind chemical elements that society needs for the industry. For example iron, lead, fluorine, sulfur, etc. Usually to get them having a mine is required, which is a vertical wells from which goes horizontal galleries. These are elongated along the seams or ore veins. In a mine the mineral matter is called ore and accompanying rock, gangue. Nowadays, many mineral deposits are being exploited opencast. This type of operation is done by blasting with dynamite. Then with the aid of shovels, minerals are loaded on a truck to the shredders.

The mineral reserves are logically limited, because of that every time it is necessary to recover the chemicals already use and prevent them from ending up in rivers and the sea, where it is almost impossible to recover them for reuse. At present, much of the iron melt in the furnace is obtained from scrap. This process is known as one example of the recycling of metals.

On the other hand, some chemicals such as mercury (thermometers and batteries), nickel and chromium (nickel and chrome industries), are very poisonous and cause mortality of fish and aquatic birds, so it also necessary to recycle instead of throwing into the aquatic environment.


Identify minerals and properties of minerals 5. (Spanish activity. Activity in English is under construction)
Crosswords 5. (Spanish activity. Activity in English is under construction)

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