|
| |
a. A hard black variety of cannel coal or brown coal, compact in texture,
having a rough fracture and dull luster that takes a good polish and is
thus used in the jewelry trade. Syn: black amberb. A sudden and forceful rush or gush of fluid through a narrow or
restricted opening; e.g., a stream of water or air used to flush cuttings
from a borehole. AGI
c. A black variety of marble.
d. Jet piercing, a thermal method of drilling large-diameter blast holes
in hard cherty iron formation (taconite); formerly used mainly on the
Mesabi Range in Minnesota, but also on the Marquette Range in Michigan.
The rotating drill head is fed a mixture of kerosene and oxygen, ignited
to direct a high-temperature flame against the rock, causing the rock to
spall into fine particles by thermal expansion. Method has been almost
totally replaced by rotary drills using tricone bits.
See also: jet hole
Source:
Dictionary of Mining, Mineral, and Related Terms
| |
|
