Liesegang Rings

> It was much quicker and easier to get the agar to 90C temperature by putting it in a microwave for 40s at 900W

Agarose gels in molecular biology labs are prepared in a similar way. (Agarose is the main component of agar.)

For an example of this that most anyone can find in nature, look up the humble agate (banded ones, most seam agates do not display the phenomena to as great of an extent.)