What are the characteristics of wollastonite?

In the field of chemistry, you’re probably no stranger to wollastonite—quite the contrary, you’re likely quite familiar with it. So, what exactly is wollastonite? Its chemical formula is Ca3[Si3O9]. It crystallizes in the triclinic system and belongs to the class of single-chain silicate minerals. It typically occurs in flaky, radial, or fibrous aggregates. Its color is white, with a slight grayish tinge. Now, how much do you already know about wollastonite? To help you better understand it, I’ve put together the following summary.

The characteristics of wollastonite are as follows:

Wollastonite is a chain-like metasilicate that also exhibits fibrous and needle-like forms. Due to its unique crystal morphology,

The crystalline structure of wollastonite determines its properties. Wollastonite boasts excellent insulation properties, as well as high whiteness, favorable dielectric performance, and superior resistance to heat and weathering. Due to these characteristics, wollastonite is widely used in fields such as ceramics, chemical industry, metallurgy, papermaking, plastics, and coatings.

The chemical molecular formula of wollastonite is CaSiO3,[1] and its structural formula is Ca3[Si3O9]. Its theoretical chemical composition is 48.25% CaO and 51.75% SiO2. Pure wollastonite is rare in nature; during its formation, Ca is sometimes partially replaced by ions such as Fe, Mn, Ti, and Sr, resulting in solid-solution minerals.[2] Wollastonite also contains small amounts of Al and trace amounts of K and Na. Due to varying temperature and pressure conditions during wollastonite formation, three polymorphic forms may occur:

① Tc-type wollastonite with a triclinic chain structure, commonly referred to as low-temperature triclinic wollastonite (α-CaSiO3);

② ZM-type wollastonite with a monoclinic chain-like structure, commonly referred to as wollastonite (α′-CaSiO3);

③ Pseudowollastonite, a triclinic three-membered ring structure, commonly known as pseudowollastonite (β-CaSiO3).

The primary industrial mineral raw material widely used is low-temperature triclinic wollastonite.

Low-temperature triclinic wollastonite belongs to the triclinic crystal system and typically occurs in needle-like, fibrous, or flaky forms. It often aggregates in fan-shaped or radial clusters, and sometimes appears as fine granular particles. The mineral is white with a slight grayish or reddish tinge, exhibiting a vitreous luster; cleavage surfaces display a pearly luster, with moderate cleavage parallelism and an angle of 74° between the two sets of cleavage planes. Its density ranges from 2.78 to 2.91 g/cm³, its hardness is 4.5 to 5, and its melting point is 1540°C. Wollastonite has a low thermal expansion coefficient, with a value of 6.5 × 10⁻⁶ mm/(mm·℃) between 25°C and 800°C. At around 1125°C, it can transform into pseudowollastonite, during which its thermal expansion coefficient increases. Additionally, impurities such as Fe and Sr are released, causing the color to change from white to cream, red, or brown. Naturally occurring wollastonite ores generally fall into two main types: skarn-type ores and wollastonite-quartz-calcite-type ores. The former are primarily found in skarn deposits and have complex mineral assemblages, often accompanied by minerals such as quartz, calcite, diopside, and garnet—typical skarn minerals. The latter are mainly found in contact-metamorphic and regional-metamorphic deposits and feature simpler mineral compositions. They can be further subdivided into three subtypes: wollastonite-quartz, wollastonite-calcite, and wollastonite-quartz-calcite. The structural features of wollastonite ores typically include two main types: dense massive ores, which exhibit fine-grained granoblastic or fibrous textures and dense massive structures, with wollastonite occurring as fine-grained, columnar, or fibrous aggregates; some exceptionally fine-grained, dense specimens even resemble jade. Coarse-grained wollastonite ores display fibrous textures and may occur in massive, breccia-like, megacrystalline, or banded forms, with coarse wollastonite crystals appearing in plate-like, columnar, bundle-like, or radiating (chrysanthemum-like) shapes.

 

Based on the summary of wollastonite provided above, we hope you now have a better understanding of this mineral. If you still have any questions, feel free to give us a call anytime!