AITA for telling my sister her ring was sketchy?

This happened a while ago and is potentially an ongoing issue, so I figured I could kick us off.

This is between me (31F) and my sister (36F).

I’m studying to become a gemologist. I’ve completed about 90% of the coursework and have a ton of new knowledge and even a decent amount of practical experience. I don’t make myself out to be an expert, but I definitely know a lot more than the average person and maybe even some jewelers.

So my sister and I were talking on Zoom and I mentioned something cool I saw recently. She said “Oh! I have this ring and it’s a star opal, what does that sound like to you?” Completely automatic, unfiltered, I replied with “Sketchy.” She got a little annoyed and told me she would get it so she could show me (through Zoom.) Thing is, star opal isn’t… real. Not in the same way that you see star sapphires. They don’t have the crystal structure or formation conditions for it. So she shows me via zoom and I say “That’s really pretty, but I really don’t think that’s opal since they don’t form that way, maybe it’s something else.” She got defensive and said that her friend got it for her in Thailand (not confidence-inspiring tbh) and that it was just something I haven’t seen before. I ended up telling her I’d look at it the next time I see her or something.

AITA for calling my sister’s ring sketchy? WIBTA if she shows it to me again of her own volition and I tell her what it actually is (probably glass)?

#amitheasshole