Cordierite is a cyclosilicate of iron, magnesium and aluminum, with the chemical formula AlSi5O18Mg2Al3Fe2. Often ferrous iron and manganese can be interchanged with magnesium or aluminum, it occurs mainly as an accessory mineral of metamorphic rocks and granites, the best known use is in the jewelry industry.
Characteristics and physical properties of cordierite
| cordierite | Characteristics and physical properties |
|---|---|
| group, class | Iron, magnesium and aluminum cyclosilicate |
| Brightness | Vitreous |
| Color | Various shades from blue to purple |
| Stripe | White |
| Tenacity | Fragile |
| Chemical formula | AlSi5O18Mg2Al3Fe2 |
| Chemical composition | Al2O3=33.6%; MgO=10.2%; FeO=5.3%; SiO2=49.4%; H2O=1.5% |
| Mohs hardness | 7 to 7.5 |
| Density or specific weight | 2.6 to 2.66 g/cm3 |
| Cleavage or exfoliation | pinacoidal, bad |
| Fracture | subconchoidal |
| crystalline system | orthorhombic |
| Way of presenting or habit | Pseudohexagonal, prismatic, massive |
| Origin and geological environment | Accessory mineral of contact metamorphic rocks |
| associated rocks | Granites, gneiss, schists |
| Associated minerals | Sillimanite, andalusite, kyanite, spinel |
| Applications | When it is of high quality it is used as a precious stone. |
The cordierite is a mineral recognized by its bluish to violet tones, depending on its higher composition in iron or manganese, this coloration will change. The stripe is white.
It is a cyclosilicate of iron, magnesium and aluminum, where Al2O3 corresponds to 33.6%, MgO is 10.2%, FeO 5.3%, SiO2 49.4% and H2O 1.5%.
Its crystallographic system is bipyramidal orthorhombic, it occurs in nature in a prismatic pseudohexagonal habit, often massive, its cleavage or cleavage is pinacoidal or bad, the fracture is of the subconchoidal type.
It has a hardness of 7 to 7.5, it has brittle tenacity and its specific weight has average values for silicate minerals, between 2.6 and 2.66 gr/cm3.
Characteristic as an accessory mineral of metamorphic rocks such as hornflens, schists or gneiss, mostly produced by contact metamorphism.
The most common use of this compound is for jewelry, when the glass presents transparency and clarity, it is also used as an ingredient for ceramic pieces.
Origin, formation and geological environment.
The most common origin of cordierite it occurs in metamorphic conditions, regional when it originates from shales or clayey rocks and forms schists or gneiss, or from contact to form cornea.
It occurs as an accessory mineral in pegmatitic and granitic rocks, sometimes the crystals grow complete with a short prismatic habit and rectangular cross section.
It is associated with minerals of the high temperature metamorphic series such as sillimanite, kyanite, andalusite and spinel, under interperism conditions it becomes chlorite and micas.
How to identify Cordierite?
A simple way to recognize the crystals of this mineral is to observe its marked pleochroism, which allows it to change color from different perspectives, between dark blue and violet, sometimes also showing yellow or colorless tones.
It is very similar to quartz when it is massive, for this reason it is very difficult to distinguish them, it also resembles corundum, but it is different due to its lower hardness.
When it has enough space to crystallize, it forms beautiful pseudohexagonal crystals, which are used for the jewelry industry.
Cordierite Uses
- It is not of great relevance for large-scale industrial use.
- It is used as an ingredient for ceramic parts of catalytic converters, however, it is easier if it is used cordierite synthetic for being of better quality and adaptable for the client.
- Its best known purpose is as a precious stone, when the crystals have high clarity and transparency, it is known as “lolita”, pleochroic blue in color, very similar to sapphire or tanzanite.
- However, despite its abundance in various countries, it is not such an attractive gem for jewelry collectors, so its price is low.
Interesting data
Its great pleochroism has given it a certain fame since ancient times, known as dichroite, which in Greek means rock of two colors, also called water sapphire or compass of the Vikings.
It was used as an ancient compass by determining the polarized waves of light, from the angles that it reflected with the mineral, it was possible to know the position of the sun, this in case of a climate with fog or clouds, which in northern Europe are very common.