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| Formula | CaSiO3 | Pyroxenoid group. Usually pure, but Mn and Fe2+ can substitute for Ca. |
| Crystal System | Triclinic | |
| Crystal Habit | Columnar and fibrous elongate grains, often with twinning | |
| Cleavage | Perfect cleavage on {100}, good cleavages on {001} and {-102} | Splitery cleavage fragments. Angles of cleavage: 84.5 degrees, and 70 degrees. |
| Color/Pleochroism | Colorless, white, greyish, often with yellowish or brownish tint. Vitreous. No pleochroism | |
| Optic Sign | Biaxial (-) | |
| 2V | 36-60 degrees | Most wollastonite has a 2V of ~40º. This can be higher for Fe-bearing samples. |
| Optic Orientation | X^c = -30 to -44 degrees Y^b ~ 0 degrees z^a = +35 to +49 degrees O.A.P. ~ (010) |
Cleavage fragments are length slow or length fast depending on orientation due to Y being parallel to fiber lenght |
Refractive Indices
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alpha: 1.616-1.645 |
Increase with Fe and Mn content. |
| Max Birefringence | 0.013-0.017 | Wollastonite resembles tremolite and pectolite, but both have a higher birefringence. |
| Elongation | Grains elongate parallel to b | |
| Extinction | Parallel | Elongate crystals display parallel extinction. |
| Dispersion | ||
| Distinguishing Features | Colorless to grey in thin sectionwith moderate to moderatly high relief. First order interference color yellow-orange. One perfect cleavage and two good cleavages producing splintery cleavage fragments. H = 4.5-5. G = 2.86-3.09. Streak is colorless or white. | |
| Occurrence | Occurs commonly as a product of contact and/or regional metamorphism in limestone and dolomite. Associated minerals include calcite, and grossular in hornfels, tremolite, epidote group members, diopside, and other Ca-Mg silicates. | |
| Editors | Sarah Martell AC '06 , Carolyn Tewksbury '07 | |
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Photomicrograph of wollastonite in plane and crossed polarized light (roll over image). Wollastonite has parallel extinction and has two good cleavages that intersect at an angle of 84º. |
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Photomicrograph of wollastonite in plane light (roll over image). Wollastonite typically has no color, and has distinct splintery cleavage in an end view. Mag. 10x. |