It is rather difficult to misidentify the allophane mineral as other types of clay due to its bluish look. Although the mineral was first described in the early 19th century, a large number of people still do not fully understand this mineral. Let’s learn more about its important facts and uses!
The Origin and Characteristics of Allophane
The first encounter with this mineral occurred in 1816 in Gräfenthal, Germany. It got its name from two Greek words “allos” and “phanos” which can be translated as “to appear like others.” The name comes from the fact that allophane was determined as another kind of mineral when metallurgists implemented the blowpipe flame test.
A large volume of allophane comes from volcanic ash and feldspars that underwent hydrothermal alteration or weather exposure. However, allophane mineral does not always come from the soil. In Silica Springs, New Zealand allophane can be found on the river bed as a deposit.
This mineral’s chemical formula is (Al2O3)(SiO2)1.3•2.5(H2O). The most common composition is 45.29% aluminum oxide, 34.70% silicon dioxide, and 20.01% water. Allophane has a molecular weight of 225.11 gm.
Its hardness level according to the Mohs scale is 3, while the mineral’s specific gravity is 2.75. The color can vary from green, blue, and yellow, to brown.
Allophane mineral has an amorphous crystal structure, meaning that the shape is unidentifiable. This crystal structure is largely caused by the mineral formation that typically occurs in mildly acidic to neutral environments (pH 5 to 7). Many experts have argued that since allophane has short-range atomic order, it should be considered a mineraloid.
To identify this clay type, modern analysts usually use infrared spectroscopy. The X-ray diffraction pattern shows broad, diffuse peaks. Another analysis method is high-resolution transmission electron microscopy. When analyzed with this method, allophane particles appear as very small hollow spherules.
Commonly Found Alongside Imogolite
In any text about allophane, you will likely find imogolite being brought up. There is always a significant possibility that both minerals are found together in nature, usually in tephra deposits. However, allophane is usually found in a larger quantity than imogolite in these deposits.
Different from allophane, though, imogolite’s chemical composition is fixed. Its chemical formula is written as (OH)3Al2O3SiOH. According to analysis, its particle appears as a hollow tubule.
Allophane’s silica and aluminum composition may vary depending on where you find it. In certain places, the mineral might have an Al/Si ratio over 4. However, most allophane deposits that you find have an Al/Si ratio ranging from 1 to 2.
What is the Use of Allophane Mineral?
How do people use this mineral? Many research findings are showing the potential of this mineral, just like any other clay mineral:
1. Helping Soil to Flourish
People simply do not know enough about the usefulness of this mineral in a conservation effort. Soils containing allophane and imogolite can be found not only in volcanic areas but also in rainforests. This type of soil can gather a huge amount of biomass because it retains a high volume of water and has accommodating physical properties.
Soil like this will not easily experience turnover because organic matters remain inside for a longer period. When applied in the garden or orchards, you will likely see a significant growth of crops. Due to its lengthy turnover period, this is possibly going to be a cheaper option in the long run.
2. Potential Use in Filtration Systems
Another possible usage of allophane is in filtration systems. A study found that soils containing allophane can filter a significant number of pathogens and heavy metals due to their chemical and physical properties. In the forest, it is very important because it helps protect the water supply.
As we face various forms of environmental damage in many parts of the earth, seeing the potential of a natural filtration system is good news. However, the real implementation requires further study so that the mining of allophane soil can be done responsibly and efficiently.
Final Thoughts
Allophane mineral is certainly more than just a bluish clay mineral. It has several potentials that have yet to be fully realized in our modern society. Further research can improve people’s understanding of this mineraloid. Without a doubt, though, we will see this commodity being increasingly popular in the future.
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