This is a thumbnail-sized specimen of Marburg Schist rock from Carroll County, Maryland, USA. This ancient rock dates from the middle to late Pre-Cambrian period (approx. 1 to 1.5 billion years ago).
Marburg schist is a bluish-gray to silvery-green, fine-grained, muscovite-chlorite-albite-quartz schist; intensely cleaved and closely folded; contains interbedded quartzites
This is some of the oldest rock in North America and dates from the time before life walked the Earth - life was mainly bacteria-like at this point in Earth's early history.
Refer to the photo. The black centimeter cube is shown for scale and is not included. You are purchasing a specimen like the one shown. Your purchase will include a labeled gemjar.