This is something I often don't touch during class. Mostly because we already have so much to go through and, I don't teach anything about crystal grids in my Reiki or Sekhem classes. There has been a request made to teach crystal grids specifically. I am working towards creating it.
That being said, this came up last night at the Student Meditation, if you didn't know this, maybe you will find it cool or useful. ICRT's creator, William Lee Rand, had created what he called World Peace Crystal Grids at the North and South pole. They are beautiful and are made of copper and have 12 double terminated crystal quartz laid through out them.
The idea is, you can send energy to both of these grids as a Reiki practitioner, no matter what level, to promote world peace. I suggest that we all give it a try. For more information, please read William's article. https://www.reiki.org/world-peace-grid-project