25x18mm Black Agate Flat Back Semiprecious Gemstone Cabochon 671x

Seems I have been selling black agate as black onyx. So I am correcting the title. I looked through these points AI gave me below, now I can't actually see through these stones. I actually don't see any lines or stratification, although they are very shiny. Anyway, they are all black, and probably agate.

AI Overview

Black agate and black onyx differ in a few ways, including:

Appearance: Black agate is usually solid in color, but can have some white or gray banding. Black onyx is always solid black and/or white, and has parallel banding. 

Lines: Black agate typically has unstructured lines that are curved or circular. Black onyx usually doesn't have lines, but when it does, they are straight and structured. 

Transparency: Black agate is translucent, meaning light can pass through it. Black onyx is opaque, meaning light can't pass through it. 

Luster: Black agate has a glass-like luster, while black onyx has a waxy luster. 

Hardness: Black agate and black onyx are both durable, measuring 6.5–7 on the Mohs scale of hardness. Black agate is slightly harder than black onyx, making it more resistant to scratches.