In addition, do some professional popularization of "cotton crack" and "old mine" in your question.

Cotton cracking: It is a very common phenomenon that natural jewelry contains cotton wool. It grows underground, under great pressure, and is inevitably squeezed in the process of continuous growth. This phenomenon will exist even if the gem is hard, especially tourmaline is a brittle gem, and there will be more ice-cracked cotton wool. Even tens of thousands of dollars of tourmaline bracelets and tourmaline carvings will have cotton wool ice cracks. Of course, there are tourmalines that don't crack cotton wool. These are used to make tourmaline rings, tourmaline bare stones and tourmaline pendants. They are the cleanest parts removed from the original stone, usually relatively small in size and the highest in price. They are sold by carat.

Old minerals and old materials: there is no such thing as real tourmaline. They are all gems bred underground for thousands of years, and there is no distinction between new minerals and old minerals. These terms are just a way to distinguish dark tourmaline from bright tourmaline. In addition, it will make people accept this dark tourmaline (usually black is not welcome).

This type of tourmaline is actually quite cost-effective. Usually the crystal is clean, but the color is not ideal. If the crystal is bright, even if it is 7.5 mm, the price can be tens of thousands, so it is quite cost-effective.