(~7.1 centimeters across at its widest)
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Dolomitic marble is a crystalline-textured metamorphic rock composed of dolomite or dolomite and calcite. Minor amounts of other minerals may be present. Dolomitic marble forms by metamorphism of dolostone or dolomitic limestones. A similar lithology with a different origin is dolomitized marble, which is a calcitic marble (having a limestone precursor) is chemically altered by fluids, resulting in dolomitization or partial dolomitization.
The sample seen here is from the Inwood Formation, a marble-bearing unit in the Cambro-Ordovician of New York State and adjacent Connecticut. Inwood marbles have been quarried as a source of cemetery headstones, building stone, and paving stone. Inwood marbles were originally marine limestones and dolomitic limestones. These precursor rocks were subjected to prograde metamorphism during the Ordovician-Silurian Taconic Orogeny and retrograde metamorphism in the Devonian. Commercial names for this material include "Tuckahoe Marble" and "Westchester Marble".
Stratigraphy: Inwood Formation / Inwood Marble, Cambrian to Lower Ordovician (= precursor age)
Locality: unrecorded / undisclosed site at or near the town of Thornwood (probably from an old quarry), southeastern New York State, USA
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Info. at:
en.wikipedia.org/wiki/Tuckahoe_marble
and
academic.brooklyn.cuny.edu/geology/powell/613webpage/NYCb...
