TWO UNUSUAL PHYLLOSILICATES FROM TALCVILLE, NY

Talcville, NY is located within the Balmat-Edwards Mining District in Edwards County, NY. Talcville is the site of the first commercial talc mine in New York State. The bedrock in this area is composed predominantly of a tremolite schist of metasedimentary origin, which has been locally altered to talc. The rocks are unusually deficient in iron, and are relatively manganese-rich. The presence of manganese is reflected by the well-known occurrence of hexagonite, a purple manganoan tremolite.

A collection of rock samples from a single locality along the Oswegatchie River was found to contain two unusual phyllosilicates. The first is a translucent, sea-green, mica that occurs in foliated masses with single crystal plates up to 4cm in diameter. In thin section, the mineral is colorless and biaxial(-) with a 2V angle of ~45°. Energy dispersive x-ray analysis of the green mica revealed that it was phlogopite containing small amounts of sodium and titanium, and totally lacking in iron. A pale green phlogopite was previously found and identified at another locality near Talcville by Ming(1971.) Ming's work suggested that the phlogopite's unusual color and crystal structure was the result of hydronium ions (H30) substituting for interlayer potassium cations. The effects of titanium and sodium were not considered in the previous study, these may play a significant role in determining the samples unusual properties.

A second dark purple phyllosilicate was found in a single thin layer, consisting of crystals up to 2 cm in width. In thin section, the mineral is strongly pleochroic (pale pink to red) and is biaxial(-) with a 2V of ~30. Preliminary energy dispersive analysis shows that the mineral has an unusual chemistry, containing calcium(~3.0 wgt. %), magnesium(~28.3%), manganese(~3.2%), potassium(~3.0%), sodium(~0.65%), and titanium(~.5%.) The sample contains approximately equal amounts of calcium, potassium and manganese. More work is needed, but preliminary results indicate that the sample is an unusual manganese-rich phlogopite.