|
|
Glossary of Rock and Mineral Terms - T
A | B
| C | D
| E | F
| G | H
| I | J
| K | L
| M | N
| O | P
| Q | R
| S | T
| U | V
| W | X
| Y | Z
- tabular
- Crystal habit describing a flat, tough, usually four sided crystal.
- talus
- A pile of rock fragments lying at the bottom of the cliff or steep slope
from which they have broken off.
- talus slope
- The large pile of rocky boulders that accumulates at the foot of a cliff,
typically by the mechanical-weathering process of frost-wedging.
- tarn
- A deep, typically circular lake that forms when a cirque glacier
melts.
- tarnish
- Property in certain minerals that cause them to discolor when placed in
certain environments. A famous example is Silver, which develops a
yellowish-black coating on its surface when exposed to hydrogen sulfide (H2S),
which is present in small quantities in the atmosphere.
- tectonic creep
- The almost constant movement of certain fault blocks that allows strain
energy to be released without major earthquakes.
- tectosilicates
- Group of silicate minerals that have all four oxygen atoms from each
tetrahedron share itself with an adjacent tetrahedron.
- tellurides subgroup
- Group of sulfides that contain one or more true metals combined with the
semi-metal tellurium.
- tenacity
- The reaction of a mineral to certain stress.
- tenebrescence
- The property that some minerals and phosphors
show or darkening in response to radiation of one
wavelength and then reversibly bleaching on exposure to
a different wavelength. This phenomenon is also called
reversible photochroism.
- tension
- Stress that stretches or extends rocks, so that they become thinner
vertically and longer laterally. Tension may be caused by divergence
or rifting.
- tephra (plural noun)
- Pyroclastic materials that fly from an erupting volcano through the air
before cooling, and range in size from fine dust to massive blocks.
- termination
- The end of a crystal face, usually referring to its base.
- terminus
- The outer margin of a glacier.
- tetragonal crystal system
- Any mineral that falls under the following specifications belongs to the
tetragonal crystal system: Three axes, two are equal in length, one is
unequal. All three axes are at 90° to each other.
- tetrahedral
- Exhibiting the shape of a tetrahedron.
- tetrahedron
- 1. Four sided polyhedron; all sides are equidimensional and triangular
shaped. Minerals shaped as tetrahedrons belong to the isometric system.
2. The building block of all silicates. It is composed of one silicon atom
equidimensionally placed around four oxygen atoms. The groups of silicates
are classified based on how the tetrahedrons join together.
- tetragonal trisoctahedron
- Synonym of trisoctahedron.
- texture
- The feel and appearance of a mineral, such as color, crystal form, and
luster.
- theory
- A comprehensive explanation of a given set of data that has been
repeatedly confirmed by observation and experimentation and has gained
general acceptance within the scientific community but has not yet been
decisively proven. See also hypothesis and scientific law.
- thermal contraction
- A form of mechanical weathering in which cold causes a mineral's
crystal structure to contract.
- thermal expansion
- A form of mechanical weathering in which heat causes a mineral's
crystal structure to enlarge.
- thermal plume
- A vertical column of upwelling mantle material, 100 to 250
kilometers in diameter, that rises from beneath a continent or ocean and can
be perceived at the Earth's surface as a hot spot. Thermal plumes
carry enough energy to move a plate, and they may be found both at plate
boundaries and plate interiors.
- thermoluminescence
- Phenomenon exhibited in certain minerals that they give off light, like a
glow, when heated. Can only be observed in a dark area. Thermoluminescent is
term used to describe minerals that emit light after being heated.
- thrust fault
- A reverse fault marked by a dip of 45º or less.
- tidal bore
- A turbulent, abrupt, wall-like wave that is caused by a flood tide.
- tide
- 1. The cycle of alternate rising and falling of the surface of an ocean or
large lake, caused by the gravitational pull of the Sun and especially Moon
in interaction with the Earth's rotation. Tides occur on a regular basis,
twice every day on most of the Earth. 2. A single rise or fall within this
cycle.
- topography
- The set of physical features, such as mountains, valleys, and the shapes
of landforms, that characterizes a given landscape.
- transformation
- The alteration of one mineral to another.
- transform motion
- The movement of two adjacent lithospheric plates in opposite directions
along a parallel line at their common edge. Transform motion often causes
earthquakes.
- transition zone
- The seismic discontinuity located in the upper mantle just beneath
the asthenosphere and characterized by a marked increase in the
velocity of seismic waves.
- translatory motion
- the movement of water over a significant distance in the direction of a
wave.
- translucent
- Describing something that is able to transmit light but not fully. Objects
can be seen through a translucent object, but they will be unclear.
- transparency
- The quality of how a mineral lets light through.
- transparent
- Describing an object that is able to transmit light through it, and if
placed in front of another object, that object can be seen as if there is
nothing interfering.
- transverse dune
- One of a series of dunes having an especially steep slip face
and a gentle windward slope and standing perpendicular to the prevailing
wind direction and parallel to each other. Transverse dunes typically form
in arid and semi-arid regions with plentiful sand, stable wind direction,
and scarce vegetation. A transverse dune may be as much as 100 kilometers
long, 200 meters high, and 3 kilometers wide.
- trapezohedral
- Shaped as a trapezohedron.
- trapezohedran
- Synonym of trisoctahedron.
- trap rock
- Rock formed from solidified lava, which usually contains pockets holding
crystals.
- triboluminescence
- Property exhibit in certain minerals which causes them to give off orange
or yellow "flashes" when sawed or struck. Minerals with this
property are triboluminescent.
- tributary
- A stream that supplies water to a larger stream.
- trichroic
- Synonym of pleochroic.
- triclinic crystal system
- Any mineral that falls under the following specifications belongs to the
triclinic crystal system: Three axes, all of them are unequal in length,
none of them are right angles to each other.
- trigonal crystal system
- The trigonal crystal system is really part of the hexagonal crystal system
and only has one minute difference (in that true hexagonal minerals have
sixfold symmetry, whereas trigonal minerals have threefold symmetry). The
trigonal crystal system, like the hexagonal crystal system, has: four axes,
three are equal in length and lie at an angle of 120° from each other. The
fourth is either longer or shorter but must be at a right angle toward the
other corners.
- trilling
- Intergrowth of three orthorhombic crystals that twin at the center and
form a hexagonal shaped crystal.
- triplet
- Gem composed of three cross-sections pasted together. The top portion,
which is the portion that is visible, consists of a naturally occurring,
valuable gem, while the bottom two portions are low-grade material, such as
glass or rock crystal.
- trisoctahedron
- 24 sided polyhedron; all sides are equidimensional. Minerals shaped as
trisoctahedrons belong to the isometric system and are referred to as
trisoctahedral.
- trunk
- An individual portion of a vein.
- trunk stream
- A large stream into which tributaries carry water and sediment.
- tsunami (plural tsunami)
- A vast sea wave caused by the sudden dropping or rising of a section of
the sea floor following an earthquake. Tsunami may be as much as 30
meters high and 200 kilometers long, may move as fast as 250 kilometers per
hour, and may continue to occur for as long as a few days.
- tube test
- Complex, scientific test which is conducted to identify a mineral. A
mineral is crushed and its powder is placed in an open or closed tube, which
is then heated; the reaction of the powder in the tube to the heat acts as a
guide for identifying the presence of certain metals in the mineral.
- tuberose
- Aggregate composed of large, oval, "bubbles" protruding from a
surface. Similar to pisolitic, but "bubbles" are protruding
instead of slightly rounded.
- tufa
- Synonym of sinter: Mineral deposit formed by mineral-rich spring water
which comes to the surface and loses its capacity to withhold the dissolved
mineral, thereby depositing it and forming a growing mound. Sometimes
misconceived as tuff.
- tufacious spring
- Spring which produces tufa.
- tuff
- Porous igneous rock composed of volcanic ash compacted together.
- tumbled
- Having been placed in a tumbler, which smoothes out and enhances the
luster of a mineral. Rocks and minerals may be naturally tumbled, if they
were smoothed and rounded from having been in a fast-flowing stream or river
for a long period of time.
- tumbler
- Machine that smoothes the surfaces and increases the luster of minerals by
"tumbling" them together in a cylindrical container that rotates,
causing them to continually bang into one another.
- tungstates group
- Group of minerals that are compounds of one or more metallic elements and
the tungstate radical (WO4). These minerals are very heavy, soft,
and brittle. The tungstates are usually categorized with the chemically
related molybdates, in which they can be partially replaced by. The
tungstates are also known as the wolframates.
- twin
- Two or more crystals that intergrow in a specific method. May also be used
in verb form, as "Two crystals may twin to form a cross."
- twinning
- Tendency of some crystals to intergrow in a distinct way or form specific,
repeated patterns. See penetration
twinning, repeated twinning,
and contact twinning.
|
