This is a thumbnail-sized specimen of Diabase rock from Carroll County, Maryland, USA. This rock dates from the Triassic period (approx. 200-250 million years ago).
This rock is also known as "Microgabbro" or "Dolerite".
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.