Small worry stone made from Mahogany Obsidian, which is black obsidian with additional coloring and patterning in dark reddish brown. Worry stones are an oval shape with a slightly concave indentation for your thumb, and are polished smooth. 

Approximately:
1.25" x 1.5"
3 cm x 4 cm

Picture is representative of the product you will receive, but may not be the exact stone. Each stone will vary slightly in color, pattern, and shape.

Secondary picture shows other worry stones available here.