From Wiki:

Diamonds sparkle because of their cut, not their flaws.

• The Role of the Cut: The cut of a diamond refers to the precise angles, proportions, and flat polished surfaces (called facets) created by a gem cutter. When a diamond is cut correctly, light enters through the top, bounces off internal walls like a mirror, and shoots back out to your eye. This creates brilliance (white light), fire (rainbow colors), and scintillation (flashes of light when the stone moves).

• The Role of Flaws (Clarity): Flaws—known as inclusions or blemishes—are natural imperfections inside or on the surface of a diamond. Instead of helping a diamond sparkle, large or cloudy flaws actually get in the way of light, making the stone look dull, cloudy, or lifeless.

• The Verdict: Even a completely flawless, rare diamond will look dull and glassy if it is cut poorly (too deep or too shallow) because the light will leak out of the bottom or sides. An expert cut is what unlocks a diamond's shine.

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Sia: My Mum & Dad used to have a jewelry business. The cut all kinds of precious and semi-precious stones, including the occasional diamond. They taught me how to cut, drill, polish, and set stones into fine settings. It was quite laborious and exceedingly frustrating whenever mistakes were made on beautiful stones.I never got that good at cutting facets properly so I hire that process out or purchase finished stones instead.

The "ancient" cutting machinery is long gone now, having broken years back with no replacement parts available. I bought new polishing equipment over the years, so I'm good with that part.

Anyway, the cardinal rule with fine gemstones is to examine it thoroughly before cutting to ensure there are no inclusions (flaws) that may break or shatter a stone in the process.

Better to have a simple polished piece without proper facets than a cracked stone that could have been gorgeous if done properly.

Anyway, that's how I know for a fact that it is not the flaws that shine, but properly cut facets.

I think you may be mixing up materials. Mildly flawed items tend to be more interesting than perfect examples of the same item. It is the flaw that gives character. Not so with diamonds or other crystals.