This lovely brooch is just under 3".  It is signed RA, indicating that the Scottish silversmith Robert Allison made the piece.  Robert Allison made jewelry during the middle of the 20th century.  The piece is also marked "Scotland" and has 3 additional markings, which were hard to capture in pictures.  One of those markings may indicate the date of the piece.  From my research and comparison of similar Robert Allison pieces, this piece was likely made in the mid 50s to early 60s. 

The piece includes a cabochon amethyst that is prong set.

This piece is in very good condition.  The closure works well, and the bar is not bent, as shown in the photos.  There are some areas of wear that are minor enough to not be seen without magnification.