The piece above is a older Dancraft cat and dog pin. They are a rare variety of andradite.
Demantoid garnets have characteristic inclusions that look like horsetails.
Demantoids were very popular in the 1800's, but are rarely used today. A demiparure is a matching set of jewelry, usually containing a necklace, earrings, and a pin. See parure . The demi-parure above is a set by Trifari . A diadem is a tiara, a circular of semi-circular piece of jewelry worn on the head.