"Tropical Optical": Iris Agate and Sterling Silver Necklace (J)
Stone: Iris Agate with black/red opal bead accents at closure
Metal: Sterling Silver (all parts)
Length: Please see photo
Closure: Small lobster claw with ring closure
This, my curious friends, is Iris Agate. Iris agate isn't a sub-type of agate, but rather refers to agates which have a very colorful optical effect: rainbow colors!
Agates which are both translucent/transparent and FINELY banded *may* show this effect if they are sliced super thinly, though finding the effect is pretty rare!
Basically there are 2 things happening:
1. Reflection: The yellows and whites you see in the last photos is what the agates look like in reflected white light. White light bounces off the SURFACE of the stone and into our eyes. This is not how you can see the rainbows. For that, you need to break up the white light.
Leading us to 2. Refraction: As white light passes THROUGH the stone, it hits the tiny, thin bands of the agate. This disruption is enough to scatter the white light, breaking it up into various rainbow colors! So, in order for you to see rainbows in your agate, you have the backlight it. This works in sunlight and lamplight (as long as it's white light).