These color change gems have always intrigued me. This example changes from purple in some lighting to a stunning teal blue much as the created alexandrite gemstones do. This one is testing as a sapphire and is also most likely created due to lack of inclusions. Without professional lab testing it is difficult to say. Though a created it is not glass it is not glass or paste. I am listing this ring as 14k though it is testing of higher content, is not holding firm at 18k but my Jeweler said it is at least 15k though it is not marked.
I tried and tried to capture the teal color this ring changes to but when photographed it still looks purple though it does turn a very teal blue in color. With this being said, this gem is bezel set which means the gem is almost certainly original to the ring as it would not be inexpensive to have a bezel setting redone. Also, The gem measures 9.7mm by 7.83mm so it is not the standard 10x8 in size.
The face of the ring is 16.8mm long by 16mm wide. I would consider this piece to be early 20th Century and possibly Antique in age. I am merely a collector, not an expert in identifying specific Era so I feel most comfortable with this assessment.
Weight 3.1 grams, yellow gold setting.