In order to learn how to mine for sand, a GM Miner must read the book Find Glass-Quality Sand. The ability does not cost any skill points, and has no effect on the skill cap. The book can be bought from the Gargoyle Alchemist NPC located in the alchemy shop in the Royal City in Ter Mur. The book costs 10,637 gold and is consumed once read.
As of Publish 68.3, GM Miners will dig up sand at every attempt provided that they are mining on a beach. Felucca spots will give you two times the amount of sand. You can expect 6-13 samples per resource grid area (8x8). Respawn times range from 10-20 minutes.