Any substance capable of lowering the melting ranges in end-stage magmatic
fluids. AGI
Said of igneous rocks that consist of 90% to 100% mafic minerals.
CF:melanocratic; ultramafic. AGI
A class of short-lived elementary nuclear particles with masses greater
than that of the neutron. Lyman
An orthorhombic mineral series, 8[(Mg,Fe)2 Si2 O6 ] ;
pyroxene group, intermediate between enstatite and ferrosilite; prismatic
cleavage; a common rock-forming mineral in intermediate to mafic igneous
rocks and high-grade metamorphosed iron formations of the Lake Superior
type; abundant in host rocks of copper-nickel ores of Sudbury, ON, Canada,
and of chromite deposits of the Bushveld complex, South Africa.
See also:pyroxene
Originally defined as a syn. of norite, but now commonly used to mean a
rock composed entirely of hypersthene; an orthopyroxenite. Not recommended
usage. AGI
See:subhedral
A texture of igneous rocks in which the greater proportion of the
crystallized minerals have subhedral forms. Hess
Peat composed mostly of disintegrated plants of hypnum, often associated
with other mosses and with intermingled rootlets of sedges and other
flowing plants. It is formed chiefly in areas where the ground is only
slightly acid, neutral, or slightly alkaline; it is brownish or drab,
light, spongy, and matted, and often laminated and porous. USBM, 5
A mineral deposit found in a deeply eroded mass of intrusive rock with few
roof pendants remaining.
See:focus
Said of the texture of an igneous rock that has crystalline components in
a glassy groundmass, the ratio of crystals to glass being between 7:1 and
5:3. Syn:merocrystalline
See:hypogene
See:hypogene
a. Said of a geologic process, and of its resultant features, occurring
within and below the crust of the Earth. CF:epigene; endogenetic.
Syn:hypogenic; hypogeal; hypogeic. AGI
b. Said of a mineral deposit formed by ascending solutions; also, said of
those solutions and of that environment. CF:supergene; mesogene.
AGI
c. A rarely used syn. of plutonic. AGI
Ore deposited from ascending hydrothermal solutions of magmatic origin.
A rock that was formed deep within the Earth under the influence of heat
and pressure. Hess
See:hypogene
Said of the texture of an igneous rock that has crystalline components in
a glassy groundmass, with a ratio of crystals to glass between 3:5 and
1:7. CF:hypocrystalline
Said of a hydrothermal mineral deposit formed at high temperatures and
pressures. CF:epithermal; hydrothermal deposit; leptothermal;
mesothermal; telethermal; xenothermal.
A conception or proposition that is tentatively assumed, and then tested
for validity by comparison with observed facts and by experimentation;
e.g., the planetesimal hypothesis to explain the evolution of the planets.
It is less firmly founded than a theory. AGI
Undiscovered resources that are similar to known mineral bodies that may
be reasonably expected to exist in the same producing district or region
under analogous geologic conditions. If exploration confirms their
existence and reveals enough information about their quality, grade, and
quantity, they will be reclassified as identified resources.
USGS, 2