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Wollastonite

earth science Maturity 7-9 Next article →

Wollastonite is a calcium inosilicate mineral that serves many vital industrial roles.

Wollastonite-91985
Wollastonite-91985

Chemically, it is written as CaSiO3. This formula tells us it is made of calcium and silicon. In a pure sample, calcium oxide makes up 48.3% of the weight. Silicon dioxide makes up the other 51.7%. Sometimes, other elements like iron, manganese, or magnesium swap places with calcium. This creates a variety of chemical combinations. Because it is so useful, it is a major commodity in global industry.

This mineral forms through intense geological processes deep underground. It usually starts when impure limestone or dolomite is subjected to high temperature and pressure. This often occurs in contact with metamorphic rocks or in skarns. A skarn is a specific type of rock formation. It can form when limestone within a sandstone is metamorphosed by an invading dike. In these cases, calcium migrates outward to react with silica. A common chemical reaction produces the mineral: CaCO3 + SiO2 → CaSiO3 + CO2. During this process, the rock loses carbon dioxide to create wollastonite.

While it looks like other minerals, its internal structure is unique.

SiO3 chains Pyrox vs Wollast
SiO3 chains Pyrox vs Wollast

For a long time, scientists classified it within the pyroxene group. This was because both groups share a silicon-to-oxygen ratio of 1:3. However, in 1931, researchers Warren and Biscoe discovered a major difference. They found that wollastonite has a different crystal structure. Specifically, it contains infinite chains of SiO4 tetrahedra. In pyroxenes, these chains repeat after only two tetrahedra. In wollastonite, the motif repeats after three tetrahedra. Because of this, it is now classified as a pyroxenoid.

The crystal structure is triclinic, meaning it belongs to a specific geometric space group. This structure remains stable even at extreme temperatures. When the mineral is molten, it maintains its tetrahedral structure up to 2000 °C. The mineral is named after William Hyde Wollaston. He was an English chemist and mineralogist who lived from 1766 to 1828. His work helped lay the foundation for much of modern mineralogy.

Global production of this mineral is quite large. In 2021, the estimated world production of crude wollastonite ore was 1,200,000 tonnes. The world's reserves are estimated to exceed 100 million tonnes. Major producers include China, India, the United States, Mexico, and Finland. In the United States, mining occurs in Willsboro and Gouverneur, New York. In 2008, the price for raw wollastonite varied between US$80 and US$500 per tonne. The cost depended on the size and shape of the powder particles.

2005wollastonite
2005wollastonite

Wollastonite is used in many different ways across various industries. In ceramics, it is a major additive, accounting for 30% to 40% of worldwide sales. It helps reduce shrinkage and gas evolution during the firing process. It also helps maintain brightness and prevents glaze defects like cracking. In the plastics and rubber industry, it accounts for 30% to 35% of sales. Here, it improves tensile strength and thermal stability. In the paint industry, it acts as a pH buffer and improves weather resistance.

WEZUWIAN WOLLASTONIT ANDRADYT 2
WEZUWIAN WOLLASTONIT ANDRADYT 2

The mineral also has important roles in construction and metallurgy. It can serve as a safe substitute for asbestos in floor tiles and roofing products. It is highly resistant to chemical attack and remains stable at high temperatures. In metallurgy, it acts as a flux for welding and a source of calcium oxide. It can even protect the surface of molten metal during steel casting. Interestingly, it is also being studied for environmental benefits. Adding it to soil can stimulate organic carbon mineralization. It is even used in a new type of cement that reduces the carbon footprint of concrete by 70%.

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File:2005wollastonite.PNG
2005wollastonite.PNG
File:Wollastonite-91985.jpg
Wollastonite-91985.jpg
File:WEZUWIAN WOLLASTONIT ANDRADYT 2.jpg
WEZUWIAN WOLLASTONIT ANDRADYT 2.jpg
File:Wollastonite-cell.png
Wollastonite-cell.png
File:SiO3 chains Pyrox vs Wollast.png
SiO3 chains Pyrox vs Wollast.png
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