The mineral vermiculite is a silicate, belonging to the group of micas, whose chemical composition is (Mg,Fe,Al)3(Al,Si)4O10(OH)∙4H2O.
Vermiculite is characterized by having golden yellow, green, brown colors, it also has a white stripe color, the shine is earthy or oily, translucent, the hardness on the Mohs scale is from 1 to 2, that is to say that the mineral is white and it can be scratched with a fingernail.
The vermiculite It occurs in laminar, tabular or pseudohexagonal crystals. It presents a perfect exfoliation, the fracture that is evident is uneven and fragile.
The system in which it crystallizes is monoclinic.
They were formed by the alteration of biotite, phlogopite and micas (muscovite) that are highly hydrated. This mineral can also be found in soils that have suffered weathering of granitic rocks.
Vermiculite has some important properties for which it is required as an industrial mineral.
Physical properties and characteristics
- Class: SILICATE
- Subclass: Phyllosilicate
- Group: Lenses
- Subgroup: Hydromica
- Geological setting: Hydrothermal alteration.
- Associated rocks: Mafic and ultramafic rocks (dunite, perixonite, peridotite), biotite schists and amphiboles.
- Mineral assembly: Vermiculite, biotite
- Chemical formula: (Mg,Fe,Al)3(Al,Si)4O10(OH)∙4H2O
- Color: Yellow, green, brown
- Luster: Oily to earthy
- Stripe: White
- Cleavage: Perfect
- Fracture: Uneven
- Tenacity: Brittle
- Hardness: 1 to 2
- Refractive index: nα= 1.525 – 1.561; nβ= 1,545 – 1,581; nγ= 1,545 – 1,581
- Fluorescence: Non-existent
- Specific gravity: 2.6
- Crystal system: Monoclinic
- Uses: Substrate in hydroponic cultivation, thermal insulation, vermiculite plates, construction material.
Geological environment
Vermiculite is formed by the alteration of biotite mainly in basic rocks, occurring near the surface.
This mineral forms by the pseudomorphic substitution of biotite as small particles in ancient soils and sediments, and at the interface between feldspar-rich and iron-magnesium-rich igneous rocks.
In the same way it is formed by the hydrothermal alteration of iron micas.
How to Identify Vermiculite
It is recognized from other micas by its yellow color and by the increase in volume when it comes into contact with heat, this is due to the fact that the water molecules found in the internal structure of the mineral evaporate when subjected to high temperatures.
Additionally, vermiculite decomposes in the presence of hydrochloric acid (HCl).
Uses and applications
There are several uses for vermiculite, among which we have the following:
The main use is as an agricultural substrate in crops.
Exfoliated vermiculite has been used for the manufacture of fabric pipes containing oil and liquid contaminants. Production of mortars or vermiculite plates as a replacement for plasterboard applied to thermal insulation or fire protection.
Ground vermiculite is used in friction material to replace asbestos, it is also mixed with clay minerals to release refractory mold and other coatings.
Exploration and exploitation
The exploration is focused on structures that contain large amounts of large biotite crystals, on ultramafic intrusive structures such as coarse-grained pyroxenites and metamorphic bodies with biotite schists.
A quality mineral required in the industry must have the following characteristics: the vermiculite particles are visible to the human eye, it is disintegrable and easily broken with a prospecting hammer, it exfoliates when subjected to high temperatures, in the field we do it with help of a propane wick.
The exploitation of this mineral has been carried out in the open sky, although there have been cases in which it has been carried out underground for small concentrations.
The removal can be done with drilling and blasting or with the help of conventional equipment such as excavator, loader and dump trucks.
The ore with the required particle size is transported to the beneficiation plant for further processing.