Butterfly Silver Onyx necklace Mexico

Butterfly necklace, looks like inlaid black onyx, has real marcasite on silver Butterfly wings. It’s pretty fancy and unique. Main pendant part is a teardrop shape with a beautiful butterfly! It’s a very Lovely piece of jewelry, unique perfect for warm summer day or night! See photos for details & measurements. Vintage necklace from Mexico. Looks like Sterling Silver but I don’t see the little 925. Don't know the designer or exact age, I am told it’s from Mexico and it’s not a newer necklace.