Rock which, because of its physical and geological characteristics, is capable of sustaining openings without any structural support except pillars and walls left during mining (stalls, light props, and roof bolts are not considered structural support).
Found on
http://www.coaleducation.org/glossary.htm
Rock which, because of its physical and geological characteristics, is capable of sustaining openings without any structural support except pillars and walls left during mining (stalls, light props, and roof bolts are not considered structural support).
Found on
http://www.rocksandminerals.com/glossary.htm
No exact match found.
