There are 2 requirements that qualify schach to be kosher:
1. It's growth is from the ground,
2. Is not mekabel tumeh.
Based on these 2 requirements it would seem completely permissible to make a solid roof on the succah made of colored crystals. Crystals, both, grow from the ground and, because they are rock, are not mekabel tumeh. Being colored, they will filter back enough light so that there is more shade than light.
Everyone seems to want to shake their heads and say but "it means" that it should have once been botanical life at one time. There is no such requirement listed in the Gemara. It seems to be obvious that schach be former plant life, but that is not written among the other requirements and seems to just be an assumption.
Thank you for all your help in my efforts to learn daf yomi.
Chaim Baruch Kaufman
Art Director/Illustrator, Chinuch.org
Dear Reb Chaim Baruch,
See the Gemara in Sukah (12a) that tells us that you cannot use animals as Sechach because we have a Pasuk (b'Aspecha mi'Gornecha u'mi'Yikvecha - Devarim 16:13) from which we learn that the Sechach must be similar to the leftovers of the threshing floor and the wine press (meaning the plant matter leftover after the useful food component has been removed). I think this Pasuk would also exclude crystals.
Kol Tuv,
Yonasan Sigler
This is not a Psak Halachah