This is a large Worry Stone, material is Hematite and it is in the shape of a heart. The approx measurements are 56 x 45 mm; thickness is approx 7 mm. 
 
Hematite is known as one of the main iron ores. The Romans saw this stone as a protection stone, as soldiers would crush the stone and rub it on their bodies before going into battle. Native Americans create war paint with this stone so it would make them invisible to their enemies. Hematite has a hardness of 6-6.5, color is black, red and rainbow. It is found worldwide.