Nice piece. So I just did a little reading on soapstone. It has different hardnesses, depending on the talc content. Your fingernail has a Moh's hardness of about 2.5. If you can scratch it with a copper penny ( Moh's 3.5 ) it is probably soapstone. If you can scratch it with a knife (Moh's 5.5) probably still soapstone. If a knife won't scratch it, then it may be serpentinite ( metamorphosed soapstone ).