Thank you for posting this. I hadn't gotten around to asking about these chips yet. I planned to send some to Robert for identification and possible comments. The chip came from me, here are some photos of the inside.

We did the shavings test also. Shavings off plastic chips stay smooth and I can't crumble them between my finger, the shavings from this chip behaved the same as clay chips. They crumbled immediately.

Could it be a clay composite? The chips all have the injection mark on the rim.