Workers have a chance to obtain Rough Black Crystal when mining Iron Ore from Abandoned Iron Mine (Depleted Iron Mine in KR Version).

Its South East of Tarif and South West of Altinova, in Mediah. Theres two OTHER NODES named similar so don't get confused (Abandoned Iron Mine Saunil District & Abandoned Iron Mine Rhutum District).

Note: There are 2 Ores your workers can mine here, Iron and Zinc however the Rough Black Crystal can only be obtained through mining the Iron Ore only! Not the Zinc - It took me a few days to figure it out.

General mining by hand I have located a few places to start

http://wttest.enjin.com/forum/m/37110298/viewthread/27035121-bdo-mining-locations-for-black-quartz-rough-crystal

Here is video about crystals -> https://www.youtube.com/watch?v=qViynyGbCiY Cheers!