Anyone who has tried it will tell you: clays are very versatile natural remedies! Whether to relieve tendinitis with a poultice, clean a wound, combat gastralgia orally or give yourself a little beauty with a mask... clays work, they even work. But where do the multiple properties of clays come from? What are the mechanisms that make them so powerful? How do they act on the body? And what major properties do they offer us?

This article was updated on 14/12/2023
Page Summary [Display]

Where do clays come from?

Rock, mineral, what about clays?

In our everyday language, when we talk about clay, we immediately think of this earth or this rock with a sticky and malleable appearance, like modeling clay, on contact with water...

If we examine these rocks more closely under a microscope, we will be able to distinguish the constituents of the rock, that is to say the clay minerals. They are invisible to the naked eye and even with a magnifying glass, but these minerals contained in clay rocks are called “phyllosilicates” in reference to their organization in sheets, from the greek phyllon, and their silica composition. To the naked eye they are then organized into superimposed strips. It is these minerals which give the rock its very particular properties…

By misnomer, we are talking about clays but keep in mind that it is the clay minerals that interest us!

Clays, the majority constituents of our soil…

Clays are constantly produced by the Earth. Our Earth, and particularly its crust, has undergone real evolutions, forming various minerals over time. Among them, the best known and found in abundance are feldspar (60%), the magnesium-iron group (17%), quartz (12%), or even micas (4%), to name only the best known. . Via mechanical but also chemical processes, these rocks which make up the earth's crust produce clays. But how ?

Rock weathering, also called erosion, can be due to the mechanical action of wind or water and even temperature. Freezing and thawing phenomena disintegrate rocks by breaking them little by little into particles. In addition, rainwater, sometimes acidic, causes the rock to rework via chemical reactions.

Thus, weather conditions cause theerosion of eruptive rock, particularly feldspars, thus creating a sedimentary rock which includes our famous clays! We find them today in the form of deposits, more or less extensive and of very different colors... Witness for example the Winikunka mountain, also called rainbow mountain, which we find in the heart of the Cordillera from the Andes to Peru.

Clays are truly witnesses to the evolution of the earth's crust...

The composition and classification of clays

We often talk about clay... But should we talk about clay or clays?

Under this general term clay, often used, lies in reality a large family...
Clay, or should I say all clays, are earthy sedimentary rocks resulting from the decomposition of mineral species. They are all composed of alumina silicates onto which minerals from the environment have been grafted. The different composition of these gives the clays their variety of colors!
White, Green, Red and even Blue... they make us dream in colors!

3 families of structural clays

Composed mainly of alumina silicates, the clays still present significant differences in arriving at their respective colors…

Depending on the minerals it contains but also on its layered structure, clay falls into a very specific clay family. The conformation of minerals takes place in the form of sheets of the order of a nanometer. Imagine that under a microscope you could distinguish different layers of superimposed lamellae... The composition of these layers, their thickness, their structure define the clay family and more precisely the type of clay we are dealing with.

Let's not forget that clays are mainly composed of alumina silicates... Thus, the sheets are formed of two types of layers, either they are made up of silica (SiO4), or they are composed of alumina (Al2O3). In the first case, silica and oxygen (O) form a tetrahedron, that is to say a volume with 4 faces. In the second case, 8-sided octahedra are composed of alumina in their center, hydroxyl (H) and oxygen in the corners. In addition to these layers forming sheets, the clay structure is interspersed withinterfoliar spaces which as their name indicates, are the spaces between separating the sheets.

The clayey soils are then distributed into three structural families :

  • the 1:1 family corresponding to a tetrahedral layer overlooking an octahedral layer. This arrangement is repeated as follows… We are talking more clearly here about kaolinites in particular.

  • the 2:1 family, here an octahedral layer is literally sandwiched between two tetrahedral layers as is the case for illite, glauconite or montmorillonite for example. Special cases exist in this family, if the aluminum is replaced by another atom, as is the case for talc, or according to the composition of the interfoliar space.

  • the 2:1:1 family, these clays are made up of two tetrahedral sheets framing an octahedral layer but in this case theinterfoliar space, that is to say the space intersecting the sheets, is filled by an octahedral sheet. Chlorite has this conformation for example.

These differences in structure and thickness will notably have a role on the cohesion between the layers, the stability of the clay and its ability to swell with water. For example, kaolinite swells less than montmorillonite because the latter experiences disorganization in the stacking of its layers, making it easier to separate them; water can more easily lodge in “empty” spaces.

Legend

An X-ray measurement of the structure of clays

The structure of a clay is measured using a method using X-ray diffraction. Kesako?

This technique is based on the diffraction of X-rays by the material passed through. A beam of X-rays encounters a material, in this case clay, which deflects the rays from their initial trajectory. This deviation varies depending on the thickness of the clay structure, the number of layers, etc.

Thus, by measuring the angles of the diffracted rays, it is possible to determine the clay family or even the clay we are dealing with!

Clay and water, a great love story…

Clay + water = colloidal solution

Let’s look at a totally chemical aspect of clays… Have you already taken the test?  In a container filled with water, pour a little bit of powdered clay and observe... The clay particles behave like drops of oil in water: suspended micelles form and, you will see... It's very surprising, they bind to each other like a magnet! It is the presence of minerals carrying negative and positive charges that causes these forces of attraction and repulsion. Thus, the clay particles naturally agglomerate but the slightest agitation of the water modifies this state and then redisperses the clay in the water... We speak of a colloidal solution.

Hello what? A colloid is a macromolecule or mineral which, when placed in water, does not form a solution as is the case when sugar is dissolved in water for example, but forms a suspension. How is this explained? The size of clay minerals is larger than the empty spaces left by water molecules (H2O)... While salt or sugar manages to slip into these “holes”, we speak of dissolution, clay minerals are not capable of this, we speak of dispersion.

Dispersed state and flocculated state

Let’s go further in our vocabulary… When the negative and positive charge exchanges stabilize, the clay aggregates flocculate. I flocculate, you flocculate, we flocculate… but yes of course! Flocculation corresponds to the deposit of clay forming at the bottom but which is capable of redispersing again in the event of agitation.

You would have understood it, two states of clay in water are observed: thedispersed state or theflocculated state ! These are two reversible states except in special conditions… heat, degradation, hydration… These states explain in particular the different reactions of the soil to climatic events. When clays are flocculated, they appear welded, allowing soil particles such as sand to form very resistant aggregates, even in heavy rain. However, if the clays are dispersed, there is no “structure” of the soils strictly speaking… The clay loses its role as “cement” and the soil will be disrupted and sensitive to erosion and climatic factors.

In conclusion, a soil that is too waterlogged will disagglomerate the clays from other mineral elements (sand, silt, etc.). The ground will then be less stable. A soil that is too dry, on the contrary, can create faults in clay soils and therefore also weaken it. Ultimately, everything is a question of balance... The desirable water content in ideally constituted soil (50% sand + 30% silt + 15% clay + 5% humus) must be around 15% to 20 %.

Clay is the cement of… soil! The ground, the ground ok, but you will see later, the colloidal properties of clay explain its astonishing therapeutic properties... (the suspense is unbearable..!)

Texture ring

For clayey soils, we can estimate the clay content by making a “texture ring”...Yes, yes, yes, you will experience it. Take a ball of earth and knead it to make a sausage.

  1. He holds ? Estimate that your land is composed of 10% clays.
  2. Can it be rounded? there is 15% clays.
  3. Can you close it in a ring despite some cracks? Lhe clays are present at nearly 30 %.
  4. In a last case, if the ring remains smooth, clays are present at 50 % !

The properties of clay

Do you remember above we talked about colloid, water and properties of clay? Tell me yesiiiiii… Well here we come, that’s it! If clay cannot dissolve in water, it is capable of fixing water by absorption, water but also a lot of things in suspension...

Absorbent power of clays

This is one of the most important powers of clay: its absorbent power ! Absorption is a passive phenomenon which, like a blotter or a sponge, allows the clay to absorb water. As we have seen, clays cannot dissolve in water, their molecules being too large to fit into water molecules... However, water can occupy the spaces available in clay molecular structures!

As we also saw above, each type of clay is made up differently. Thus, if we were to classify them, taking into account their different structures, montmorillonites would have the strongest absorption power, followed by illites and finally kaolinites. 

This absorption capacity gives clays a power justifying its use in numerous poultices for treating wounds by absorbing pathological fluids like pus for example. Another use is practical in a house for absorb bad odors.

To better visualize it, imagine clay soil drying out... it is cracking! But you just need to add a little water for it to regain its smooth and malleable appearance, as is the case for the potter who kneads his material.

Adsorbent power

The phenomenon ofDsorption is different from that of aBsorption. It's a active phenomenon, it manifests itself by the capture of molecules on active sites or by the existing attraction between positively charged molecules (cations) and those negatively charged (anions).

Thus, the clays are capable of fixing substances on their surface and chemical compounds. This is calculated using the cation exchange capacity of clays (CEC). 

For example, studies have shown that clays attracted bacteria or even toxins, proving their usefulness during digestive problems for example.

Was this article helpful to you?

  

Average grade: 4.6 ( 327 votes)

Bibliography

Publication: Hernot, F. (2006). Clay, its use in the pharmacy. http://dune.univ-angers.fr/fichiers/20073109/2016PPHA5426/fichier/5426F.pdf

La Compagnie des Sens and its teams do not encourage self-medication. The information and advice provided comes from a reference bibliographic database (books, scientific publications, etc.). They are given for information purposes, or to suggest avenues for reflection: they should in no case replace a diagnosis, consultation or medical follow-up, and cannot engage the liability of the Compagnie des Sens.