A method of roof control whereby the natural strength of the roof strata
is maintained by relieving pressure in working areas and controlling
transference of load to abutments that are clear of workings and roadways.
The method consists of causing certain coal pillars to yield in small
amounts. See also:double packing
The differential stress at which permanent deformation first occurs in a
material. Syn:yield stress; yield strength. Roark
The stress at which a material exhibits a specified deviation from
proportionality of stress and strain. An offset of 0.2% is used for many
metals. See also:yield point
a. The lowest stress at which extension of a tensile test piece increases
without increase in load. It is determined by observing the fall of the
testing lever and checked by a pair of dividers on the original gage
length. Many materials do not indicate a defined yield stress and in such
cases the proof stress is used. See also:working stress;
high-tensile steel; mild steel; yield point. Hammond
b. Minimum stress required to shear (that is, exceed elastic recovery) a
suspension, such as the dense media used in mineral concentration.
Pryor, 3
Acronym and abbrev. for yttrium-iron garnet. USBM, 7
A monoclinic mineral, (Mg,Al)8 Si4 (O,OH)20 ; purple;
highly pleochroic; in a quartz-yoderite-kyanite-talc schist at Mautia
Hill, Kongwa, Tanzania.
Dark-blue corundum from Yogo Gulch, MT. Schaller
a. An interconnecting link between the twin cylinders of a hydraulic-feed
diamond drill through which the action of the hydraulic-feed cylinders is
transmitted to the drill rods and bit. Long
b. A clamp fitted to the casing at the collar of a drill hole, which when
anchored by means of wedge bolts prevents grout pressure from forcing the
casing out of the hole. Long
Nodule; occurs at Forest of Dean, U.K.
A term which has been proposed (instead of Westphalian) for the Coal
Measures strata between the Lanarkian and the Staffordian. Nelson
A triclinic mineral, (Ba,Sr)2 TiMn2 (SiO4 )2
(PO4 ,SO4 )(OH,Cl) ; forms orange-brown tabular crystals or
stellate groups; occurs in an alkali pegmatite at the Noda-Tamagawa Mine,
Iwate prefecture, and the Taguchi Mine, Aichi Prefecture, Japan.
Walnut-to almond-size pebble with an opal center; ironstone covered with a
thin band of opal, or hollow; near Yowah station, western Queensland,
Australia. A subvariety of boulder opal.
See:gadolinite
A rare-earth element that has a bright silvery luster, is soft, malleable
and quite ductile. Symbol, Yb. Occurs with other rare-earths in a number
of rare minerals. Commercially recovered from monazite sand. Has a
possible use in improving the mechanical properties of stainless steel;
few other uses have been found. Handbook of Chemistry and Physics, 3
A calcium-iron garnet containing a small amount of yttria. A variety of
andradite. Fay
A possibly hexagonal mineral, (Y,Th)2 Si2 O7 ; olive
green tarnishing to orange-yellow; occurs in Texas.
A rare-earth element that has a silvery-metallic luster. Symbol, Y. Occurs
in nearly all of the rare-earth minerals. Recovered commercially from
monazite sand and from bastnasite. Widely used: in color television tubes;
to reduce the grain size in chromium, molybdenum, zirconium, and titanium;
to increase the strength of aluminum and magnesium alloys; as a deoxidizer
for vanadium and other nonferrous metals; in nuclear technology for its
high neutron transparency. Handbook of Chemistry and Physics, 3
Synthetic; Y3 Al5 O12 ; has useful magnetic
properties. Actually not a true garnet and should not be confused with any
of the silicate minerals called garnets in the garnet group of minerals.
Manufacture of yttrium-aluminum garnets is a commercial use of yttrium.
Used in lasers and in microwaves and other electronic applications.
Acronym and abbrev., yag. Handbook of Chemistry and Physics, 2
A variety of garnet containing a small amount of yttrium earths.
Syn:yttrogarnet
Synthetic; Y3 Fe5 O12 ; has useful magnetic
properties. Actually not a true garnet and should not be confused with any
of the silicate minerals called garnets in the garnet group of minerals.
Manufacture of yttrium-iron garnets is a leading commercial use of
yttrium. Used as electronic transmitters, as filters for selecting or
tuning microwaves, and as transmitters and transducers of acoustic energy.
Acronym and abbrev., yig.
Bennett; CCD, 2; Handbook of Chemistry and Physics, 2
An orthorhombic mineral, (Y,Th,Ca,U)(Ti,Fe)2 (O,OH)6 ; also
contains Th, U, Fe; radioactive; black altering to a dull brown coating;
in granite pegmatites.