Featured Pendant / Gemstone identification?

I saw this pendant on ebay with some really blurry photos and hardly much of a description, and took a risk. Got it for a little over the price of the gold.

Details

• 18K YG
  
• ~1.6g
• 0.5" diameter
• Color changing
  • Violet Inside
  • Red under UV light
  • Robin-Egg blue in sunshine

My amateurish analysis

• The two solder points under the pendant suggest to me that this actually came from a ring or a beret?
• Most likely a color-changing synthetic sapphire due to the red glow in UV light.
  
• Age unk - interesting plate cannetile work though.
• EDIT: in starting to look at my own photos I'm questioning whether it is even gold. yikes! see - outside photo

Thoughts on what I have?

 

Might be alexandrite. I suspect an earring dangle.

 

It's definitely a color change sapphire, lab grown. It is not such an expensive stone that it would be reserved for use with fine gold. The chunkiness of this mount makes me question representation as 18K.

 

I’m leaning towards this as well. I didnt want to scratch the bottom for an acid test but i think I’m going to have to.

 

Update: i tested it and its 14k. I can see why she thought it was 18k though, the solution definitely took a while to dissolve it. Might be 15k, etc.

 

Earring dangle does seem quite likely, as @Ownedbybear said.