A smooth, rounded piece of rock, cylindrical in shape, which may drop out of the roof of a mine without warning. The origin of this feature is thought to be the remains of the stump of a tree that has been replaced by sediments so that the original form has been rather well preserved.
Iron Cornish bucket used to hoist ore and miners to the surface.
2.205 pounds. When describing percentages of minerals in bulk tonnage, kgs are often used. To wit, a company might report 4% copperÉ which is to say 4 kg of copper per tonne of rock.
A variety of peridotite; the most common host rock of diamonds.