Hello. I've has this stone for many years. It weighs 29oz (seems heavy for the size). Dimensions: 4.5"L x 3"W x 2.5"H. It's blackish/green with some embedded white, smooth shiny surface, lots of lines.
Looks like a mixture of hematite and quarts. Hardness test on the areas and a streak test would help. check out the treads on these tests. Might even be magnatite~ magnetic?