There are many kinds of obsidian.

But obsidian is not a single black-proof, which is a misunderstanding.

Rainbow eye, crescent moon, moon eye and ice obsidian are not all black-proof.

The phenomenon you mentioned is rainbow-eyed obsidian,

Reference materials help you extract it.

Black diabase is usually black, but brown, gray and a little red, blue and even green can also be seen. It may also be all monochrome, stripes or spots. Some inclusions give Blackstone a metallic luster, while the bubbles or crystals inside produce a "snowflake" effect (that is, snowflake Blackstone) or are regarded as a flashing rainbow color. ..... is a lot of color circles formed naturally on the basis of the full moon cat's eye obsidian. The more colors, the rarer and the better the quality. Because some can best appear in dozens of colors, it is named rainbow-eyed obsidian.

The economic value of obsidian is not very high, and there are not many imitations in general.

Besides, you're wrong to suspect black agate. Black agate is multicolored to light, which is only possible by artificial optimization. The color optimization of black agate on a bead will not be multicolored, so there is no need to be so careful. The original optimized black agate is of low value.

If you have any questions, just ask.

I hope the answer can help you.