gold tool mortar and pestle is octagonal shaped, thick walled, agate mortar with pestle. both have highly polished grinding surface.. available in different sizes : 
-> mortar and pestle 2.5" : material : black agate stone, size : 2.5" 
-> mortar and pestle 3" : material : black agate stone, size : 3"
 -> mortar and pestle 3.5" : material : black agate stone, size : 3.5"
 -> mortar and pestle 4" : material : black agate stone, size : 4"