This is a ceramic pendant modeled after a gemstone/rock. There is dark glass in the center.
The glaze is a brown color with gray accents with an antique brass bail.
It is ready to be strung on your own necklace that will fit through the roughly 3mm bail.
Please note that the coloring might be somewhat different since this is a homemade item and glazes fire differently each time.
Also note that ceramic pieces that are not in a full bezel are usually glazed on the back of the piece as well. Due to the firing process, there may be tiny pin pricks on the back. These are as expected and are sanded smooth.