From the way you have described it, the seller's I.D. on it seems to be correct. Some handgun grips are made of horn, mostly water buffalo, and the process, as I have heard described, is to cut the horn lengthwise, heat it and flatten it out, then reheat and put in molds and press it to whatever result you want. This is a guess on my part as to your plaque and I'm sure soje of the other posters will come up with more detailed facts. If you could narrow down the age of your plaque it may narrow down the composition of it. Bakelite is another guess guess but I believe Bakelite is not translucent.