Tatnic Hill Formation

Sulfidic sillimanite schist, sillimanite schist and gneiss, biotite gneiss; minor amphibolite, calc-silicate gneiss and marble.
State Massachusetts
Name Tatnic Hill Formation
Geologic age Ordovician or Proterozoic Z
Lithologic constituents
Major
Metamorphic > Schistsulfidic sillimanite schist, sillimanite schist
Metamorphic > Gneisssillimanite schist and gneiss, biotite gneiss; minor calc-silicate gneiss
Minor
Metamorphic > Amphibolite
Metamorphic > Metasedimentary > Calc-silicate-rock
Metamorphic > Metasedimentary > Metacarbonate > Marble
Comments Part of Nashoba Zone (Silurian and Older Rocks). The age of the Putnam Group, including its Tatnic Hill Formation, is considered to be Late Proterozoic(?) based on the 730 my age of the Fishbrook Gneiss in MA and the 440 my age of the Hedgehog Hill gneiss intruded into the upper part of the younger Brimfield Group (Pease, 1989) per MA009.
References
NGMDB product
Counties Worcester