Wollastonite in Plastics: Properties, Grades, Loading and Selection

Wollastonite is a naturally occurring calcium metasilicate mineral (CaSiO3, CAS 13983-17-0) whose crystals grow as needles, and that needle shape is the reason compounders use it as a reinforcing filler rather than as a simple extender. A filler with an aspect ratio of 5 to 30 transfers load in a way that a blocky particle such as ground calcium carbonate cannot, so the question that matters for a formulator is where that shape pays off in a real compound. Among mineral plastic additives, wollastonite sits between the cheap extenders and the true fibres: it costs less to process than glass fibre, brings less anisotropy, and still raises stiffness in ways a platelet mineral cannot match.

This page covers wollastonite's identity, its reinforcement mechanism, its grades and surface treatment, which polymers use it, how loading is set, how it compares with talc, mica, kaolin and glass fibre, how filler content is measured, whether it is asbestos, and the EU and US food-contact rules that apply. Grade-specific loading is set by trials against the producer's data sheet, not a single universal number, and this page says so plainly rather than inventing a figure the record does not support.

Wollastonite key figures

• Identity: CaSiO3, CAS 13983-17-0, EC 237-772-5
• Aspect ratio: 5 to 30 (acicular, needle-shaped)
• Hardness and density: Mohs 4.5 to 5, density 2.8 to 2.9 g/cm3
• EU food contact: FCM No 613, Ref 95905, no specific migration limit (SML)
• Carcinogenicity classification: IARC Group 3 (Monograph vol. 68, 1997)

What Is Wollastonite?#

Wollastonite is a naturally occurring calcium inosilicate mineral with the formula CaSiO3, formed where impure limestone or dolomite is recrystallised by heat and pressure in metamorphic rock and skarn deposits. It belongs to the mineral filler group that includes talc, mica, kaolin and calcium carbonate, but its crystal habit sets it apart: those minerals form flat platelets or blocky particles, while wollastonite grows as needles. It is one of the mineral fillers for plastics that the hub groups by particle shape.

Identity: CAS number, formula and composition#

Wollastonite is registered as CAS 13983-17-0 and EC 237-772-5, has the formula CaSiO3 and a molecular weight of 116.16, and when pure consists of 48.3 % calcium oxide and 51.7 % silica. It is also known by the synonyms calcium metasilicate and natural calcium silicate, and its commercial grades appear under the trade names NYAD and NYGLOS (Imerys), Vansil (Vanderbilt Minerals) and Tremin (Quarzwerke). The 48.3/51.7 split is the theoretical composition of the pure mineral; a commercial grade's actual purity is stated on its own data sheet.

Physical properties that matter in a compound#

The four properties that decide how wollastonite behaves in an extruder are its aspect ratio of 5 to 30, its Mohs hardness of 4.5 to 5, its density of 2.8 to 2.9 g/cm3 and the alkaline pH of 8 to 10 of a water slurry.

Physical values are mineral-property ranges from our source library. Grade data sheets give narrower values for each product.

Aspect ratio governs how much load a particle carries before it pulls out of the resin, so it is the value most compounders check first. Mohs hardness of 4.5 to 5 places wollastonite above ground calcium carbonate (Mohs 3) and well above talc (Mohs 1) on the abrasion scale; that difference is a selection consequence, not a measured wear figure, so screws, barrels and downstream tooling running wollastonite compounds are normally specified with wear protection. The alkaline slurry pH of 8 to 10 is why an acid-sensitive co-additive, such as certain heat stabilizers, has to be checked for compatibility before it is combined with wollastonite. Particle size, surface area and oil absorption as general filler concepts are treated under filler properties; the aspect ratio concept, the length-to-thickness number separating a filler from a reinforcement, has its own glossary entry.

What is another name for wollastonite?#

Wollastonite is also called calcium metasilicate or natural calcium silicate, and it is sold under trade names including NYAD and NYGLOS (Imerys), Vansil (Vanderbilt Minerals) and TREMIN (Quarzwerke). These trade names identify the brand owner, not a guarantee of identical performance across every grade in that family; each grade's particle size, aspect ratio and surface treatment are stated on its own data sheet.

What Does Wollastonite Do in a Plastic Compound?#

Wollastonite does four things in a plastic compound, and the needle shape is what separates it from an ordinary extender:

• Raises tensile and flexural strength through load transfer from the resin to the particle.
• Adds thermal and dimensional stability, including heat deflection temperature and reduced warpage.
• Displaces resin, lowering the polymer content of the compound.
• Replaces asbestos historically, in friction products and other reinforced systems.

A reinforcement, by definition, is a filler with a high aspect ratio that raises tensile strength and modulus because load transfers from matrix to particle by interfacial shear; a low-aspect-ratio extender mainly reduces resin cost without that strength gain.

How needle-shaped particles reinforce a polymer#

A needle-shaped particle carries load because stress transfers from the polymer into the particle through interfacial shear along its length, the same mechanism that makes a short glass fibre work and a spherical filler ineffective. Kelly and Tyson (1965) and Cox (1952) set out the shear-lag description of that transfer, and Halpin and Kardos (1976) turned it into the equations compounders still use to estimate the modulus of a filled polymer. Fu, Feng, Lauke and Mai (2008) and Pukánszky's (1990) interfacial model extended the same framework to particulate and short-fibre composites generally.

Shape sets the ceiling on that effect. Spheres and near-cubic particles, aspect ratio near 1, reinforce very little because they present no length along which shear can build. Platelets, aspect ratio roughly 5 to 100, raise stiffness, heat deflection temperature and barrier properties. Needles and fibres raise strength, modulus and heat deflection temperature further, but bring anisotropy and warpage, since particles orient with flow during moulding. Wollastonite, at an aspect ratio of 5 to 30, sits inside the needle class but far short of a true fibre: glass fiber reinforced plastics use E-glass fibres from about 20 up to more than 1,000, so the same shear-transfer mechanism at a much higher aspect ratio makes a glass-fibre grade stiffer again. No modulus or strength value for a wollastonite-filled compound is stated here, because none exists in the source record.

Stiffness, heat deflection and dimensional stability#

Wollastonite raises stiffness and heat deflection temperature and holds a moulding closer to its nominal dimensions, which is why mineral-reinforced grades are chosen where a glass-fibre grade would warp. This is a function classification from the source record, not a measured value, and the actual gain depends on the grade, the loading and the base resin.

• Stiffness: needle orientation along the flow direction increases flexural modulus relative to an unfilled resin.
• Heat deflection: mineral loading raises the heat deflection temperature at which a part deflects under a standard load, though the exact gain is grade-specific.
• Dimensional stability: a moderate aspect ratio reduces the shrinkage differential between flow and cross-flow directions compared with a higher-aspect-ratio fibre, the practical meaning of "low warpage" here.

Wollastonite as a resin extender#

Every kilogram of wollastonite in a compound replaces a kilogram of polymer, but because its density of 2.8 to 2.9 g/cm3 is roughly three times that of a polyolefin, the saving per litre of finished part is much smaller than the saving per kilogram. Cost per kilogram of compound is the sum of each ingredient's weight fraction multiplied by its price; cost per litre is that figure multiplied by density, so a filler that is cheap by weight but dense by volume lowers cost per kilogram more than it lowers cost per litre. That arithmetic is what every formulator runs before treating a mineral purely as an extender. Converters who buy filler as a concentrate rather than as loose powder work with filler masterbatch.

Wollastonite Grades: Aspect Ratio, Particle Size and Surface Treatment#

Wollastonite grades differ in three variables that a data sheet always states: median particle size, aspect ratio and whether the surface has been treated with a silane. Particle size spans 1 to 500 µm and aspect ratio spans 5 to 30 within the same mineral, so two grades from one producer can behave very differently.

Brand families only. Grade codes, particle sizes and aspect ratios come from each producer's current data sheet.

Request quotes for wollastonite: specify median particle size, aspect ratio, surface treatment, volume, polymer and country through the plastic additive supplier finder.

High-aspect-ratio (acicular) grades versus powder grades#

The same mineral is milled into two families: high-aspect-ratio acicular grades that keep the needle intact for reinforcement, and low-aspect-ratio powder grades that behave more like a blocky extender and cause less anisotropy. The source record gives only the overall 5 to 30 aspect-ratio span for the mineral, so no fixed numeric boundary separates the two families; each grade's position on that span is stated on its data sheet.

Top cut, the particle size at which 98 % of the distribution passes (d98), is what controls impact strength and surface defects within either family, since a small number of oversized particles can act as stress concentrators regardless of the average particle size.

Silane-treated wollastonite and why fillers are coupled#

Because wollastonite is a silicate, an aminosilane or methacrylsilane bonds to its surface, which is why treated grades exist and untreated grades disperse but do not couple. Silanes suit siliceous fillers, including silica, glass, wollastonite and kaolin; they are largely ineffective on calcium carbonate, where titanates or stearic acid are used instead. An integral-blend silane is added at 0.2 to 1.0 wt% of the total mix; a pretreatment coats the mineral surface before compounding, at a minimum of 1.0 % for a 1-10 µm filler, at least 1.5 % below 1 µm, and 0.75 % for a 10-20 µm filler, based on monolayer coverage estimates. This chemistry is covered under filler surface treatment.

Named coupling agents include APTES (sold as Silquest A-1100 or Dynasylan AMEO), GLYMO and MEMO; where APTES or MEMO treat surfaces for food-contact plastics, both carry an EU 10/2011 specific migration limit of 0.05 mg/kg. Compounders should treat the surface-treatment level as part of the formulation, not a fixed mineral property. The agents themselves, including maleated polyolefins, are covered under coupling agents for filled and reinforced plastics.

Which Plastics Use Wollastonite?#

Our source library documents wollastonite mainly in mineral-reinforced polyamide and in polypropylene compounds. Both routes are pulled by the same end market, additives for automotive plastics, and this reflects what is documented, not an exhaustive market picture; no share of any polymer's total filler consumption is claimed.

Mineral-reinforced polyamide (PA6 and PA66)#

Mineral-reinforced polyamide is the clearest home for wollastonite: where a glass-fibre grade would warp, compounders use a mineral filler, typically wollastonite, calcined kaolin or mica, at a loading in the region of 30 to 40 % to hold the part flat. This is a handbook range, not a specific data-sheet value, so it should be confirmed against the grade sheet before use. The glass-fibre alternative runs 15 to 50 % glass fibre in PA6/PA66, with 30 % (GF30) a standard reference point; PA6 melts at 215-218 °C and PA66 at 264 °C, and moisture uptake in either polymer reduces modulus regardless of filler. Low-warpage grades built on this principle are compared under mineral fillers for nylon.

The rest of the additive package a polyamide needs, including its copper heat stabilizers, is covered on additives for nylon (polyamide).

Polypropylene and polyolefin compounds#

In polypropylene, wollastonite competes directly with talc: the US Geological Survey lists it, with bentonite, kaolin and mica, as a substitute for talc in plastics. The needle shape adds strength in a direction talc's platelet shape cannot match, but wollastonite's Mohs hardness of 4.5 is well above talc's Mohs 1, so it is correspondingly more abrasive to processing equipment. Talc carries a separate surface property that does not automatically transfer: its Lewis-acid surface sites can catalyse polymer oxidation at high temperature, which is why talc-filled polypropylene is normally formulated with a stronger antioxidant package. That interaction is documented for talc, not wollastonite, and this page does not state or imply that wollastonite is antioxidant-neutral. Loading levels across the mineral set used in polypropylene are compared on fillers for polypropylene.

The mineral wollastonite most often replaces or is replaced by is talc in plastics.

Thermosets, fluoropolymers and other systems#

Wollastonite also appears in thermoset compounds and in filled fluoropolymers, but our source library carries no loading levels or performance data for those systems, so this page names them without giving numbers. GLYMO is documented as the coupling agent for glass and mineral fillers in epoxies, polyesters and polyurethanes generally, placing wollastonite inside the same surface-treatment logic used for other mineral and glass reinforcements in thermosets. Filled fluoropolymer product listings exist commercially, but they are supplier listings, not sourced facts. Thermoset filler practice more broadly is covered on additives for epoxy resins and composites.

How Much Wollastonite Goes into a Compound?#

No single loading applies to wollastonite: mineral fillers as a class sit between 0 and 50 wt% of a plastic product (Hahladakis and colleagues, 2018, via Chea and colleagues, 2025), reinforcements between 15 and 30 wt%, and mineral-reinforced polyamide is usually built in the region of 30 to 40 %. Published loadings for wollastonite specifically are scarce, which is why this page states class-level bands rather than a single wollastonite-only number.

Five variables set the actual level in a given formulation:

• Part stiffness and heat target: a higher modulus or heat deflection temperature target pushes loading up.
• Warpage and anisotropy tolerance: tight dimensional tolerances limit how much acicular filler a design can accept.
• Screw and tool wear budget: wollastonite's Mohs 4.5 to 5 hardness sets the abrasion ceiling a tool steel and screw can tolerate.
• Melt viscosity: higher loading raises melt viscosity, narrowing the processing window.
• Density and cost per volume: wollastonite is roughly three times denser than a polyolefin, so the cost-per-litre benefit is smaller than the cost-per-kilogram benefit.

Dosage for thermoplastics is expressed in weight percent (wt%), converting from parts per hundred resin (phr) as wt% = phr of the ingredient divided by the sum of all phr, times 100; PVC and rubber typically use phr, polyolefins and engineering plastics use wt%. Grade-specific loadings come from the producer's data sheet, and the final level is set by trials against the target property. The full set of dosage bands across additive classes, from ppm-level stabilizers to 10-70 % fillers and plasticizers, is collected under additive dosage levels in plastics.

Wollastonite versus Talc, Mica, Kaolin and Glass Fibre#

Wollastonite is the needle among the common mineral fillers: talc, mica and kaolin are platelets, ground calcium carbonate is blocky, and glass fibre is a true fibre, so wollastonite delivers part of a fibre's strength with less of the warpage. The comparison below covers shape and physical properties only; no comparative modulus or impact-retention figure is given, since none exists in the source record.

Physical values are mineral-property ranges from our source library. Grade data sheets give narrower values for each product.

Among the platelets, the highest aspect ratio in this group belongs to mica in plastics, reaching 20 to 100 against wollastonite's 5 to 30, though it delivers stiffness and barrier properties rather than the tensile reinforcement a needle provides.

The finer platelet, used where surface finish and electrical properties matter more than raw reinforcement, is kaolin in plastics.

At the other end of the shape scale sits the blocky extender, which reinforces the least of any filler in this comparison but costs the least to process: calcium carbonate in plastics.

How Is Filler Content and Its Effect Measured?#

Filler content is measured by ashing or thermogravimetry to ASTM D5630 and ISO 3451, and the effect of that filler is read from heat deflection temperature (ASTM D648 / ISO 75), tensile properties (ISO 527, ASTM D638-22) and notched impact strength (ASTM D256-26, ISO 180). No pass or fail value for a wollastonite compound exists in the source record; the end point for any of these tests is the product specification, not a value stated here.

Four properties, each with its own standard, cover what a formulator checks:

• Ash and filler content: ASTM D5630 and ISO 3451 (ashing), thermogravimetric analysis (TGA) and density methods, compared under ash content and filler content testing.
• Heat deflection temperature: ASTM D648 or ISO 75, at 0.455 or 1.82 MPa, 2 °C/min, to 0.25 mm deflection on a specimen at least 3 mm thick; a comparative index, not a design value.
• Tensile properties: ISO 527-1/-2 and ASTM D638-22, similar but not directly equivalent, described on tensile testing of plastics.
• Notched impact strength: ASTM D256-26 (J/m) and ISO 180 (kJ/m2), on a specimen of 63.5 by 12.7 by 3.2 mm; the property a high filler loading typically costs first, per impact strength (Izod, Charpy).

Is Wollastonite Asbestos? Safety, IARC and Dust Limits#

No, wollastonite is not asbestos. It is a calcium silicate, and the International Agency for Research on Cancer places it in Group 3, not classifiable as to its carcinogenicity to humans (Monograph volume 68, 1997). What is regulated around any mineral filler is airborne workplace dust, not the mineral itself.

Is wollastonite asbestos?#

Wollastonite is not asbestos: asbestos minerals are fibrous serpentines and amphiboles, while wollastonite is a calcium inosilicate whose crystals are acicular rather than asbestiform. The regulatory direction of travel reinforces the distinction: the US Environmental Protection Agency's final rule of 28 March 2024 (Federal Register 89:21970) banned chrysotile asbestos, and the US Geological Survey expects that ban to raise wollastonite demand in friction products as a substitute mineral. "Asbestos-free" is never stated here as a blanket claim about every commercial grade; the facts stated are the IARC classification and the regulatory action, not a marketing claim.

IARC classification and occupational dust exposure#

The exposure that matters with any mineral filler is airborne dust in the compounding plant, not the finished article, in which the filler is locked into the polymer. Of 742 GHS notifications recorded for wollastonite, 642 carry no hazard classification, while a minority notify H319 (eye irritation) and H335 (respiratory irritation), a notification count rather than a single harmonised classification. For scale, respirable crystalline silica carries a binding EU occupational limit of 0.1 mg/m3 under Directive (EU) 2017/2398 amending Directive 2004/37/EC, and a US OSHA permissible exposure limit of 50 µg/m3 with a 25 µg/m3 action level under 29 CFR 1910.1053; wollastonite is not crystalline silica, and these limits show only the order of magnitude mineral-dust control aims at. No Proposition 65 listing for wollastonite appears in the source record, and none is claimed here.

Is Wollastonite Allowed in Food-Contact Plastics?#

In the EU, wollastonite is listed in Annex I of Regulation (EU) No 10/2011 as FCM substance No 613 (Ref 95905) with no specific migration limit; in the US, the position is documented only partially. A food-contact plastic containing it still has to meet the general limits that apply to every substance on the Union list.

EU: Regulation (EU) No 10/2011 and REACH Annex V#

On the REACH side, wollastonite carries no registration dossier under EC 237-772-5, because naturally occurring minerals that have not been chemically modified are exempt from registration under Annex V of Regulation (EC) No 1907/2006, a pattern ECHA's CHEM database also records for kaolin, mica, dolomite, montmorillonite, feldspar, nepheline syenite and limestone. The exemption applies to the untreated mineral; whether a silane-treated grade keeps it is not answered in the available record and is not asserted here. The registration duty and its exemptions are set out under REACH and plastic additives.

Under Regulation (EU) No 10/2011, the overall migration limit is 10 mg/dm2 (60 mg/kg for infant articles) and the generic specific migration limit where none is set is 60 mg/kg; Article 9(2) restricts nanoforms of any listed substance to those explicitly authorised in Annex I. FCM numbers and migration limits are explained in full on EU 10/2011.

United States: what is and is not confirmed#

The US position is less clear-cut than the European one: 21 CFR 178.3297 lists calcium silicate among the mineral fillers usable as colorants for polymers, at a level limited to what the colouring effect requires, but the source record does not confirm that this entry covers natural wollastonite specifically, so this page states the entry and not a conclusion. No FDA clearance beyond that entry, no TSCA-specific status and no Proposition 65 listing for wollastonite appear in the record; see the methodology and fact-checking process for how every figure here is checked.

Who Supplies Wollastonite for Plastics, and What Does It Cost?#

Wollastonite for plastics comes from a short list of producers: Imerys (NYCO, with the NYAD and NYGLOS brands), Vanderbilt Minerals (Vansil), Quarzwerke (TREMIN) and Wolkem. World mine production outside the United States was an estimated 1.1 million tonnes in 2024: China about 800,000 tonnes, India 120,000 tonnes, Mexico 95,000 tonnes, per the US Geological Survey's Mineral Commodity Summaries 2025. The US mines wollastonite only in New York State, from two companies; plastics and rubber accounted for 25 to 35 % of US wollastonite sales in 2009. The segment's place in the wider plastic additives market is covered separately.

• Imerys (NYCO): brands NYAD and NYGLOS; Paris-headquartered, 2023 revenue EUR 3.794 billion, portfolio also includes talc, carbonates and kaolin.
• Vanderbilt Minerals: brand Vansil.
• Quarzwerke: brand TREMIN.
• Wolkem: no specific brand recorded in the source data.

Plants and certifications by company are listed in the directory of mineral filler suppliers for plastics.

Among those producers, Imerys also supplies talc, carbonates and kaolin alongside its wollastonite line.

The USGS does not publish a wollastonite price; acicular and surface-treated grades reportedly sell at a premium over untreated powder. For context only, never as a wollastonite price, the USGS's 2024 estimated US unit values for related minerals, ex-works, were talc USD 330/t, ground mica USD 300/t dry, ground barite USD 220/t and kaolin USD 160/t. The one mineral filler here with a tracked price series is the calcium carbonate filler price guide. Buyers should compare grades by particle size, aspect ratio and surface treatment, not by brand name.

Request quotes for wollastonite: specify median particle size, aspect ratio, surface treatment, volume, polymer and country through the plastic additive supplier finder.

Compare all 12 mineral fillers side by side on the fillers for plastics hub.

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What Else Is Wollastonite Used For, Outside Plastics?#

Most of the world's wollastonite never sees a polymer: ceramics, friction products, coatings and agriculture take the larger share, and plastics and rubber accounted for only 25 to 35 % of US sales in 2009. The rubber share of that figure is covered separately under fillers for rubber and TPE. The sections below name each non-plastics use briefly, since they sit outside the scope of a plastics reference.

Ceramics, coatings and friction products#

In ceramics, wollastonite is used because it supplies calcium oxide and silica without releasing volatiles on firing, and in friction products its needles reinforce brake and clutch materials. The same EPA chrysotile asbestos ban of 28 March 2024 (Federal Register 89:21970) that affects asbestos-containing talc is expected to raise wollastonite demand in friction products, where it has long served as a substitute reinforcing mineral. Firing temperatures, shrinkage figures and glaze recipes fall outside this site's scope.

Agriculture and soil amendment#

Wollastonite is also sold as a soil amendment and as a feedstock for enhanced rock weathering, which is why a search for the mineral returns garden retailers alongside industrial producers. This reference makes no agronomic, carbon-sequestration or health claim about that use; it names the use and states plainly that it falls outside scope.

Is wollastonite a rare mineral?#

Wollastonite is not rare as a mineral, but commercial deposits are concentrated: world mine production outside the United States was about 1.1 million tonnes in 2024, with China at 800,000 tonnes, India at 120,000 tonnes and Mexico at 95,000 tonnes, and the only US mines are in New York State.

What is wollastonite used for?#

Wollastonite is used as a reinforcing filler in plastics and rubber, as a flux and body material in ceramics, as a reinforcement in friction products and coatings, and as an agricultural soil amendment.

Is wollastonite a safe material?#

The International Agency for Research on Cancer places wollastonite in Group 3, not classifiable as to its carcinogenicity to humans, and most CLP notifications carry no classification, while a minority notify eye and respiratory irritation, so the control point is airborne dust during compounding rather than the finished plastic part.

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Every figure on this page is checked against primary sources; see our methodology and fact-checking process.