a. Metallic elements or alloys in finely divided or powder form.
Henderson
b. A general term applied by drillers, bit setters, and bit manufacturers
to various finely ground metals, which, when mixed, are commonly used to
produce sintered-metal diamond bit crowns. Also called powdered metal;
powder metal. Long
a. Newc. An argillaceous stone, shale, and sandstone.
b. Staff. See:ironstone
A marble suitable for use as polished dimension stone; e.g., the Vermont
metamarble. CF:orthomarble; metalimestone.
A metal ceramic consisting of high Cr.Al2 O3 .
Osborne
a. A mineral that has become virtually amorphous owing to the breakdown of
the original crystal structure by internal bombardment with alpha
particles (helium nuclei) emitted by radioactive atoms within the mineral.
Many green zircons, esp. those from Sri Lanka, which are Precambrian in
age, and have thus had over 800 million years of this internal
bombardment, owe their low refractive index and density to this cause, and
may be termed metamict zircons. Anderson
b. Said of a mineral containing radioactive elements in which various
degrees of lattice disruption and changes have taken place as a result of
radiation damage, while its original external morphology has been
retained. Examples occur in zircon, thorite and several other minerals.
Not all minerals containing radioactive elements are metamict; e.g.,
xenotime and apatite are not. AGI
The process of disruption of the structure of a crystal by radiations from
contained radioactive atoms, rendering the material partly or wholly
amorphous. AGI
A mineral whose crystal structure has been disrupted by radiation from
contained radioactive particles. AGI
a. The product of dehydration of montmorillonite at 400 degrees C.
Hey, 2
b. A dehydrated smectite.
Pertaining to the process of metamorphism or to its results. AGI
See:aureole
An ore deposit that has been subjected to great pressure, high
temperature, and alteration by solutions. It may have become warped,
twisted, or folded, and the original minerals may have been rearranged and
recrystallized.
A collective term for the various processes by which minerals or mineral
assemblages are locally segregated from an initially uniform parent rock
during metamorphism; e.g., garnet porphyroblasts in fine-grained mica
schist. AGI
Migration, by diffusion, of materials from one part of a rock mass to
another during metamorphism. Diffusion may involve chemically active
fluids from magmatic sources, hot pore fluids, or fluids released from
hydrous minerals or carbonates. Ionic diffusion in the solid state may
also occur. AGI
A set of metamorphic mineral assemblages, repeatedly associated in space
and time, such that there is a constant and therefore predictable relation
between mineral composition and chemical composition. It is generally
assumed that the metamorphic facies represent the results of equilibrium
crystallization of rocks under a restricted range of externally imposed
physical conditions; e.g., temperature, lithostatic pressure, and water
pressure. Syn:mineral facies
The intensity or rank of metamorphism, measured by the amount or degree of
difference between the original parent rock and the metamorphic rock. It
indicates in a general way the pressure-temperature environment or facies
in which the metamorphism took place. For example, conversion of shale to
slate or phyllite would be low-grade dynamothermal metamorphism
(greenschist facies), whereas its continued alteration to a
garnet-sillimanite schist would be high-grade metamorphism
(almandine-amphibolite facies). Syn:metamorphic rank
See also:high-rank metamorphism
See:overprint
Any rock derived from preexisting rocks by mineralogical, chemical, and/or
structural changes, essentially in the solid state, in response to marked
changes in temperature, pressure, shearing stress, and chemical
environment, generally at depth in the Earth's crust. AGI
Water driven out of rocks by metamorphism. Stokes
The mineralogical, chemical, and structural adjustment of solid rocks to
physical and chemical conditions that have generally been imposed at depth
below the surface zones of weathering and cementation, and that differ
from the conditions under which the rocks in question originated.
AGI
A triclinic mineral, CaV2 O6 .2H2 O ; pearly to dull
yellow; a dehydration product of rossite.
-< ò?O rAO j+< 2 DICTIONARY TERMS:metasandbergite See:metaheinrichite
[\B]metasandbergite[\N]