a. Said of a mineral deposit formed later than the enclosing rocks.
b. Produced on or near the Earth's surface, e.g., epigenetic valleys, etc.
c. In ore petrology, applied to mineral deposits of later origin than the
enclosing rocks or to the formation of secondary minerals by alteration.
An orthorhombic(?) mineral, (Cu,Fe)5 AsS6 (?) ; metallic
gray; forms prismatic crystals resembling arsenopyrite implanted on barite
at the Neugl#1.uck Mine near Wittichen, Germany.
The marine bottoms to a maximum depth of 20 fathoms (36.6 m).
An apophysis or tongue of an intrusion which is detached from its source.
Also spelled epiphesis. See also:tongue
In oceanography, plankton found in depths of less than 100 fathoms (183
A monoclinic mineral, Ca[Al2 Si6 O16 ].5H2 O ;
zeolite group; dimorphous with goosecreekite; forms radiating spherical
aggregates of prismatic crystals in cavities in basalt and andesite, or
with beryl in pegmatites.
A triclinic mineral, Na2 (Nb,Ti)2 Si2 O9 .nH
2 O ; forms soft, pearly white rectangular plates in curved folia in
the Julianehaab district of Greenland and the Lovozero alkali massif, Kola
a. Induced orientation of the crystal lattice of an electrodeposit at the
plane of contact with the undisturbed underlying metal. ASM, 1
b. Orientation of one crystal with that of the crystalline substrate on
which it grew; e.g., halite growing on a cleavage plane of mica because
the mesh of the net of halite nearly coincides in shape and size with the
pseudohexagonal net of the mica substrate. Adj: epitactic, epitaxic,
epitaxial. CF:distaxy; topotaxy; syntaxy.
Said of a hydrothermal mineral deposit formed within about 1 km of the
Earth's surface and in the temperature range of 50 to 200 degrees C,
occurring mainly as veins. Also, said of that depositional environment.
CF:hypothermal deposit; mesothermal; leptothermal; telethermal;
According to Grubenmann's classification of metamorphic rocks (1904), the
uppermost depth zone of metamorphism, characterized by low to moderate
temperatures (less than 300 degrees C) and hydrostatic pressures with low
to high shearing stress. Modern usage stresses pressure-temperature
conditions (low metamorphic grade) rather than the likely depth of zone.
CF:mesozone; katazone. AGI
a. The formal geochronologic unit, longer than an age and shorter than a
period, during which the rocks of the corresponding series were formed.
b. A term used informally to designate a length (usually short) of
geologic time; e.g., glacial epoch. AGI
An orthorhombic mineral, MgSO4 .7H2 O ; bitter tasting;
forms efflorescences of prismatic crystals, botryoidal masses, or
incrustations on cave and mine walls from oxidizing sulfide minerals; also
lacustrine deposits, mineral springs, and fumaroles. Syn:epsom salt;
bitter salt; hair salt. See also:kieserite
An unsheathed explosive incorporating cooling agents, which is equivalent
in safety (relating to the ignition of methane-air mixture) on a
charge-weight basis to an explosive having a sheath of cooling agents
around it. Abbrev. for equivalent-to-sheathed explosive. BS, 12
equal-errors cut point
The density at which equal portions of the feed material are wrongly
placed in each of two products of a specific-gravity separation.
Syn:wolf cut point
The separation size at which equal portions of the feed material are
wrongly placed in each of two products of a sizing operation.
Particles possessing equal terminal velocities. They are the oversize
material and form the underflow of a classifier. See also:Stokes' law;
terminal velocity. Nelson
equalization of winding load
The balancing of the weight of the winding rope, which varies considerably
during a winding cycle. See also:balance rope; winding; winding drum.