This photo shows garnets within the Waits River Formation. Garnets are by no means unusual in Massachusetts: regional metamorphism associated with repeated episodes of Appalachian mountain building (called "orogenies") has produced garnets all over the place-- In New England, they predominantly grew in place during such events during metamorphism.
What makes these garnets special is another common feature: Inclusion trails. In many instances, when the chemical-reaction between pre-existing minerals that produces a garnet occurs during metamorphism, the garnet grows around minerals in the rock that are "left over" from before the metamorphic event-- these minerals are preserved in the garnet, and their orientation (what we call "fabric") is also preserved-- in many ways, such garnets create a protected "time capsule" in the rock-- preserving older tectonic fabrics that can be dated with new geochronological methods, allowing for greater precision and accuracy in figuring out just how the northern Appalachians were formed, yielding insight into how continents, and mountain chains, are created.
