Cracked soap stone

Hi all,

Yesterday I got to try out my new soapstone. I put it on the stainless steel grill from the (cold start), no divider plate in between.

Unfortunately for me, I had an overshoot in temp, reaching 790oF/420oC on the surface (measured with IR thermometer). I turned down the heat and eventually started searing when the stone was 700oF/370oC). Still on the high side.

After letting the KJ cool over night with the soapstone in it, I started cleaning this morning. Unfortunately for me, i found that the stone had already cracked..

Do I have a faulty product, or is it really that prone to overheating?

Thanks