Calcite on Fluorite

This specimen consists of a yellow core fluorite with purple delineations on which rather stout acicular calcites haphazardly formed. Noting the previous labels you will see this piece was in the Seaman Museum followed by being in the R Peter Richards collection. Those that know him know that Pete Richards is one of the world’s foremost experts on crystal shapes and the phenomena that influence them. The prior label has a note ” twins?”.  Thus I endeavored to study the calcites, which do not typically twin as acicular crystals. My best guess is that the question was directed at the shared axis of the crystals on the far bottom right of the first photo. I do not know if Pete decided whether they are twinned, and it is a very difficult call for me. The provenance of the piece and its attractive presentation certainly support the asking.

Locality: Mahoning #1 Mine (Minerva), Cave in Rock District, Hardin County Illinois

Composition: Calcium Carbonate and Calcium Fluoride