This material dealed on the gemstone-market under the name “leopard skin jasper” does originate from a mine somewhere in “Chihuahua”. (If somebody knows something about the exact place of origin of this material please give me a note).
This jasper is a silicified rhyolithe - a silicic acid-rich volcanic rock. It is composed of a multiplicity of small, usually inside yellow and outwardly greenish colored globulites, which are embedded in a grey matrix. Because of different hardnesses in the rock it is difficult to polish this material.