The hot needle test is no longer a perfect guide. There are synthetics that look and feel very real. And pass the sniff test.
A popular faux ivory is phenolic.
Even some of the older 'plastics' look very real. I have a pair of (not ivory) faux stag grips on my Ruger Single Six. They have been there over 40 years and have taken on a nice patina just like real ivory or antler would.
I have made some non-gun related items from phenolic faux ivory and sold for high dollar. It is very nice stuff.