Glossary of Rock and Mineral Terms - B
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- backarc basin
- A depression landward of a volcanic arc in a subduction zone,
which is lined with trapped sediment from the volcanic arc and the
plate interior. See also forearc basin.
- backarc spreading
- The process by which the overriding plate in a subduction zone
becomes stretched to the point of rifting, so that magma can
then rise into the gap created by the rift. Backarc spreading typically occurs
when the subducting plate sinks more rapidly than the overriding plate moves
- The portion of a beach that extends from the high-tide line inland to
the sea cliff or vegetation line. Swash reaches the backshore only during
- The section of a floodplain where deposits of fine silts and clays settle
after a flood. Backswamps usually lie behind a stream's natural levees.
- The presence color zoning lines, or "bands", in some minerals.
Rocks with this characteristic are described as being "banded"
- banded iron formation
- A rock that is made up of alternating light silica-rich layers and
dark-colored layers of iron-rich minerals, which were deposited in marine
basins on every continent about 2 billion years ago.
- barchan dune
- A crescent-shaped dune that forms around a small patch of vegetation,
lies perpendicular to the prevailing wind direction, and has a gentle, convex
windward slope and a steep, concave leeward slope. Barchan dunes typically
form in arid, inland deserts with stable wind direction and relatively little
- barrier island
- A ridge of sand that runs parallel to the main coast but is separated from
it by a bay or lagoon. Barrier islands range from 10 to 100 kilometers in
length and from 2 to 5 kilometers in width. A barrier island may be as high as
6 meters above sea level. barrier reef A long, narrow reef that runs parallel
to the main coast but is separated from it by a wide lagoon.
- Having to do with the base.
- basal cleavage
- Type of cleavage exhibited on a horizontal plane of a mineral by way of its
base. Minerals with basal cleavage can sometimes be "peeled", like
minerals of Mica group.
- basal sliding
- The process by which a glacier undergoes thawing at its base,
producing a film of water along which the glacier then flows. Basal sliding
primarily affects glaciers in warm climates or mid-latitude mountain ranges.
- The dark, dense, aphanitic, extrusive rock that has a silica
content of 40% to 50% and makes up most of the ocean floor. Basalt is the most
abundant volcanic rock in the Earth's crust.
- 1) The top and the bottom "closing points" of a crystal. A base
exists only in minerals that belong to the hexagonal, orthorhombic,
tetragonal, and trigonal crystal systems. Also known as basal pinicoid
(synonym to base).
2) Matrix or foundation of a crystal.
3) Chemical substance that is either a hydroxide, carbonate, or metal oxide
that has the ability to turn litmus paper blue, and the ability to react with
acids to form salts. Bases are alkaline and have a bitter taste.
- base level
- The lowest level to which a stream can erode the channel through
which it flows, generally equal to the prevailing global sea level.
- Constructed of alkaline components. When seen in the composition of a
mineral, it refers to the hydroxyl radical.
- A round or oval depression in the Earth's surface, containing the youngest
section of rock in its lowest, central part.
- A massive discordant pluton with a surface area greater than 100
square kilometers, typically having a depth of about 30 kilometers. Batholiths
are generally found in elongated mountain ranges after the country rock above
them has eroded.
- baymouth bar
- A narrow ridge of sand that stretches completely across the mouth of a bay.
(Also called bay bar and bay barrier.)
- The part of a coast that is washed by waves or tides, which cover it
with sediments of various sizes and composition, such as sand or pebbles.
- beach drift
- 1. The process by which swash and backwash move sediments along a beach
face. 2. The sediments so moved. Beach drift typically consists of sand,
gravel, shell fragments, and pebbles. See also longshore drift.
- beach face
- The portion of a foreshore that lies nearest to the sea and regularly
receives the swash of breaking waves. The beach face is the steepest part of
- bead test
- Complex, scientific test which is conducted to identify a mineral. A mineral
is crushed and mixed into a borax flux, and is heated until a glassy bead
forms. The bead is then touched by the crushed mineral powder and one of
several colors appears on the bead, depending on the metallic elements of the
mineral. The colors are different in most cases when heated with an oxidizing
and reducing flame, as well as when the bead is hot and cold.
- 1) Rock mass of one type surrounded by a different type of rock. 2) A
deposit of granular rock caused from erosion of solid rock.
- The division of sediment or sedimentary rock into parallel
layers (beds) that can be distinguished from each other by such features as
chemical composition and grain size.
- bed load
- A body of coarse particles that move along the bottom of a stream.
- bed rock
- Layer of solid rock underneath the soil.
- Benioff-Wadati zone
- A region where the subduction of oceanic plates causes earthquakes,
the foci of which are deeper the farther inland they are.
- beta rays
- Form of electromagnetic radiation in which the electromagnetic waves are
composed of uncombined electrons
- A low, narrow layer or mound of sediment deposited on a backshore
by storm waves.
- biogenic chemical sediment
- Sedimentary rocks derived from living organisms. Common examples include
fossiliferous limestones and coal.
- biomass fuel
- A renewable fuel derived from a living organism or the by product of a
living organism. Biomass fuels include wood, dung, methane gas, and grain
- Crystal shape in form with a plane dividing a crystal into two pyramids base
to base. Crystals exhibiting this are described as bipyramidal.
- bipyramidal hexagon
- Six sided polyhedron with all sides protruding out of the top and bottom
points, forming a wide center. A bipyramidal hexagonal prism has a straight
center. Crystals of this shape are a bypyramid hexagon.
- Any of a group of solid and semi-solid hydrocarbons that can be
converted into liquid form by heating. Bitumens can be refined to produce such
commercial products as gasoline, fuel oil, and asphalt.
- Consisting of hydrocarbons (such as coal) and materials formed from them.
- bituminous coal
- A shiny black coal that develops from deeply buried lignite through
heat and pressure, and that has a carbon content of 80% to 93%, which makes it
a more efficient heating fuel than lignite.
- Crystal habit describing flat, elongated, "knife-like" crystals.
Like those of Kyanite
- blowpipe test
- Complex, scientific test which is conducted to identify a mineral. A mineral
fragment is placed in a cavity on a charcoal block, and a horizontal flame is
sent towards the fragment on the charcoal using a blowpipe. Depending on the
mineral, a different reaction takes place. Certain metals have a
characteristic color when flamed, and if the mineral being tested contains
such a metal, the charcoal turns that color behind the fragment. Some minerals
form a metal bead after being flamed, others give off fumes, and a few
- body wave
- A type of seismic wave that transmits energy from an earthquake's focus
through the Earth's interior in all directions. See also surface wave.
- boiling point
- The temperature that it takes a substance to start boiling after being in a
- To combine, by means of chemical reaction, with another atom to form a
compound. When an atom bonds with another, it either loses, gains, or shares
electrons with the other atom. The link between atoms to form a secure
- Group of minerals that are compounds of one or more metallic elements
combined with the borate radical (B2O3). This group
forms two sub-groups, the Hydrous borates and the Anhydrous borates.
- Industrially used chemical which is an anhydrous form of sodium borate (Na2B4O7)
used in the manufacture of glass and ceramics. It is interesting to note that
there is a mineral Borax (Na2B4O7 · 10H2O),
and it is different than the borax chemical, for it contains water. The
mineral Borax is an ore of the chemical borax. See also Kernite.
- Aggregate resembling a cluster of grapes. Also known as globular. Rounded
agglomerations of botryoidal aggregates are smaller than reniform
agglomerations and considerably smaller than mammilary agglomerations.
- Synthetic gems created from molten liquids placed in tear shaped molds to
crystallize, leaving them with a tear-like form. Mostly applied to synthetic
Rubies and Sapphires.
- Bowen's reaction series
- The sequence of igneous rocks formed from a mafic magma,
assuming mineral crystals that have already formed continue to react with the
liquid magma and so evolve into new minerals, thereby creating the next rock
in the sequence.
- braided stream
- A network of converging and diverging streams separated from each
other by narrow strips of sand and gravel.
- Man-made alloy of copper and zinc. In the olden times, any alloy of copper
was known as brass. Most brass of the olden days was an alloy of copper and
tin. See also bronze.
- A wall built seaward of a coast to intercept incoming waves and so protect a
harbor or shore. Breakwaters are typically built parallel to the coast.
- A clastic rock composed of particles more than 2 millimeters in
diameter and marked by the angularity of its component grains and rock
- breeder reactor
- A nuclear reactor that manufactures more fissionable isotopes than it
consumes. Breeder reactors use the widely available, non-fissionable uranium
isotope U-238, together with small amounts of fissionable U-235, to produce a
fissionable isotope of plutonium, Pu-239.
- 1. Referring to cut: A type of cut used for certain gemstones.
2. Referring to luster: Synonym of adamantine.
- Form of tenacity which describes a mineral that gets hammered and results in
a fine powder or small crumbs. Minerals that are not brittle are referred as
Nonbrittle minerals. Brittle minerals leave a fine powder if scratched, which
is the way to test a mineral to see if it is brittle
- brittle failure
- Rupture of rock, a type of permanent strain caused by relatively low stress.
- "Bronze" is a collective term describing any metallic alloy that
range in color from light yellow to orange. Many, if not most alloys described
as "bronze" are of copper and tin. See also brass.
- burial metamorphism
- A form of regional metamorphism that acts on rocks covered by 5 to 10
kilometers of rock or sediment, caused by heat from the Earth's interior and lithostatic