I've only got one of those now
I swapped with John, who had two amethyst ones, so now we have one of each colour, each.
I can see it's not bark which has been used to create the texture on your piece, but the basic design of a partially cased textured rectangular base is very similar.
MH got the idea of using bark from Timo Sarpaneva, (the originator of using bark to make moulds) and Geoffrey Baxter got the idea from Michael Harrris.
The '70s were still a time of loads of experimentation and cross-fertilisation and sharing of ideas between artists.