As far as I know, ironwood is going to be a little harder than the mammoth ivory, but the M/I will hold up fine in there with your keys and things. I have a natural (antique) ivory scaled pen knife that has spent a lot of time in three generation's pockets and it's in great shape. It's got some dings and scratches but is just fine. Mammoth ivory is as hard or slightly harder than elephant ivory, depending on the amount of mineral infiltration.