hag principle

The system under which a skilled miner employs an unskilled helper.
CTD

haiarn

In Wales, a term for iron.

hailstone bort

Variety of bort built of concentric shells of clouded diamond and
cementlike material. See also:bort

hair copper

See:chalcotrichite

hair pyrite

See:millerite

hair salt

Common name for efflorescences of hairlike, acicular, or fibrous crystals
of epsomite or other hydrous sulfates in caves and old mine workings.
See also:alunogen

hairstone

Quartz thickly penetrated with hairlike crystals of rutile, actinolite, or
some other mineral. CF:hedgehog stone

hair zeolite

May be natrolite, scolecite, or mesolite. Fay

half-and-half plane

Scot. In a direction midway between plane course and end course.
See also:half-course

half bearings

Bearings such as are used on railway cars where the load is constantly in
one direction and is sufficiently heavy to hold the journal against the
bearing. Crispin

half blinded

Scot. Two ends driven off a plane, one on each side and not opposite each
other by half their width. Fay

half-cell

An electrode immersed in a suitable electrolyte designed for measurements
of electrode potential. ASM, 1

half-course

A drift or opening driven at an angle of about 45 degrees to the strike
and in the plane of the seam. See also:half-and-half plane

half end

York. See:horn coal

half headers

Term applied to material that amounts to a large cap piece. They are used
by sawing a header in two and placing one or more timbers under the half
header on the same side of the track. Two timbers are generally placed
under the half header and the end allowed to extend out over the haulage.
The term half header should not be applied to regular cap pieces.
Kentucky

half-life

a. The time in which one-half of the atoms in a radioactive substance
disintegrate. Lyman
b. The time in which the quantity of a particular radioactive isotope is
reduced to one-half of its initial value. Syn:half-period

half-marrow

Newc. Youngsters, of whom two do the work of one loader. Fay

half-period

See:half-life

half-round nose

See:medium-round nose

half set

In mine timbering, one leg piece and a collar. Fay

half-value distance

The horizontal distance between the points of maximum and half-maximum
values in a symmetrical anomaly, usually either gravity or magnetic. It is
useful in estimating the depth of the geologic feature that causes the
anomaly. AGI