Kimberlite is a igneous rock that is formed deep down in the Earth's mantle zone. It contains a variety of exotic minerals and gemstones in small xenocryst form. Kimberlite is an extremely old rock that is rarely found near the surface and is commonly associated with deposits of diamonds - the world's richest diamond mines are found in Kimberlite deposits called "pipes". Besides diamonds, Kimberlite also contains olivine, garnet, diopside, spinel, serpentine, perovskite, epidote, barite, celestine, and many other minerals.
This material comes from late Jurassic period deposits near Tompkins City, in New York, USA. It has a dark grey color with various pale or translucent inclusions and xenocrysts. These pieces have been polished on one side and are thick slices.
Refer to the photos. The black centimeter cube is shown for scale and is not included. You are purchasing a specimen like the one shown.