English: Wollastonite skarn from the Precambrian of New York State, USA. (4.8 centimeters across at its widest)

Wollastonite is a calcium pyroxenoid mineral having the chemical formula CaSiO3 (calcium silicate). This is wollastonite skarn rock, composed of coarsely-crystalline wollastonite blades. This specimen is actually a wollastonite ore that derives from the Valentine Mine, an active wollastonite mine/quarry in New York State.

The Valentine Mine is located at the intrusive contact between marbles of Grenvillian age (1.13 to 1.16 Ga) and syenites of the Diana Complex (1.118 Ga). The wollastonite skarn is synchronous with the intrusion of Diana Complex syenites (see Gerdes & Valley, 1994), so it also dates to 1.118 Ga (late Mesoproterozoic). Published studies have shown that the Valentine wollastonite skarn formed by channelized infiltration of silica-rich hydrothermal fluids into calcitic marbles. This is the most common geologic process by which wollastonite forms (calcite + silica = wollastonite + CO2). Intense alteration of rocks (in this case, originally marble) by such hot, silica-rich fluids is called hydrothermal metamorphism. If chemical alteration is the principal metamorphic process (as in this deposit), the rocks are said to have been metasomatized (= altered by metasomatism). "Skarn" is the general term for metasomatized rocks and many contact metamorphosed rocks.

Age: late Mesoproterozoic, 1.118 Ga; granulite facies metamorphism during the Ottawan phase of the Grenville Orogeny at ~1.05 Ga (small-scale kink folding is present in this specimen, the result of that metamorphic event)

Locality: Valentine Mine (Gouverneur Talc Company No. 4 Quarry) (wollastonite mine), ~0.75 to 1 mile from the southern side of Lake Bonaparte, ~3.5 air miles southwest of Harrisville, northern Lewis County, northern Adirondack Mountains (northwestern Lowlands, near the Lowlands-Highlands boundary), northern New York State, USA

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Info. partly synthesized from:

Basu, A.R. & W.R. Premo. 2001. U-Pb age of the Diana Complex and Adirondack granulite petrogenesis. Proceedings of the Indian Academy of Sciences (Earth and Planetary Sciences) 110: 385-395.

Gerdes, M.L. & J.W. Valley. 1994. Fluid flow and mass transport at the Valentine wollastonite deposit, Adirondack Mountains, New York State. Journal of Metamorphic Geology 12: 589-608.