In case you missed it a couple of years ago I wrote about the French Open and brick dust here. Full members get full access to the archives. Happy Sunday. —Jason
Composition of a clay court at Roland-Garros
1- Red brick dust: 1 - 2 mm
2- Crushed white limestone: 6 - 7 cm
3- Clinker (coal residue): 7 - 8 cm
4- Crushed gravel: at least 30 cm
5- Drain
And then there’s chalk… https://www.chesterton.org/a-piece-of-chalk/
Delightful!