Wollastonite

Wollastonite’s primary significance lies in its industrial utility; it does not feature prominently in art, mythology, or cultural traditions. Its name commemorates William Hyde Wollaston, reflecting a legacy of scientific discovery rather than cultural symbolism.

• Wollastonite is one of the few naturally occurring minerals with a pure calcium silicate composition.
• It exhibits perfect cleavage, allowing it to split easily along specific planes.
• Unlike many silicates, wollastonite is highly resistant to acids and bases, making it exceptionally durable in harsh environments.
• Major deposits are found in the United States, Finland, India, China, and Italy.
• The mineral’s fibrous form is sometimes mistaken for asbestos, but it is non-toxic and safe for industrial use.

CaSiO₃ is the chemical formula for wollastonite, indicating it is composed of calcium, silicon, and oxygen. This pure calcium silicate structure is central to its mineralogical identity and industrial performance.

Wollastonite crystallizes in the triclinic system, forming single chains of silicon-oxygen tetrahedra. Its elongated, bladed, and fibrous crystals reflect this atomic arrangement, and the perfect cleavage on [100] is a direct result of its structural geometry.

• Hardness: 4.5–5 on the Mohs scale
• Color: White, gray, or pale green
• Luster: Vitreous to pearly
• Specific Gravity: 2.86–3.09
• Cleavage: Perfect on [100]
• Fracture: Splintery
• Transparency: Translucent to opaque

Wollastonite is typically found in contact metamorphic rocks, especially skarns formed by the alteration of impure limestones or dolomites through silica-rich fluids. Major deposits are located in New York and California (USA), Finland, India, China, and Italy. It is commonly associated with minerals such as garnet, diopside, vesuvianite, and calcite, reflecting its formation in high-temperature, chemically active environments.

• Synonyms: Tabular spar, wollastonite-1A, silicate of lime
• No major varieties are recognized, though polytype designations (such as wollastonite-1A) may be used in scientific contexts.

Wollastonite’s combination of low thermal expansion, chemical resistance, and fibrous structure makes it invaluable as a filler and reinforcement in ceramics, paints, plastics, and rubber. It is used as a flux in metallurgy to lower melting points and improve product quality. Its stability at high temperatures allows for applications in refractory materials and specialized industrial processes where durability and dimensional stability are critical.

• Look for white to pale green, elongated or fibrous crystals with a pearly sheen.
• Test for perfect cleavage on [100]—specimens split easily along this plane.
• Wollastonite is non-fluorescent and exhibits a splintery fracture, distinguishing it from similar minerals.
• Commonly found in skarn rocks alongside garnet and diopside.

Wollastonite specimens should be handled gently due to their splintery fracture and perfect cleavage, which can make them prone to breaking. Store in padded containers away from moisture and corrosive chemicals. Clean with a soft brush or cloth; avoid harsh acids or bases, although the mineral itself is resistant to chemical attack. Displaying fibrous aggregates may require extra support to prevent fragmentation.

Notable wollastonite specimens originate from the Monte Somma, Vesuvius, Italy—its type locality—and from large deposits in New York, USA, which have supplied industrial-grade material for decades. While not famed for museum-quality crystals, these localities are celebrated for their historical and economic importance in mineralogy and industry.