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Glossary Of Meteorite Terms & Definitions
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Welcome to the Meteorites Australia "Glossary Of Meteorite
Terms & Definitions".
Italicised words are
included in the list of Terms & Definitions.
Ablation - is the stripping of melted material from the
surface of a meteor as it moves through the Earth's atmosphere. -
Achondrite - (a-kon-drites) meteorites which do not
contain chondrules. Many of these specimens originate from
larger 'parent bodies' such as the Moon, Mars or an asteroid.
Some Achondrites may also be melted or transformed Chondrites. -
Asteroid - small planet like bodies that orbit the sun lying
mostly in the region between the orbits of Mars and Jupiter.
Their diameters range from a few metres to hundreds of
kilometres. -
Ataxite - iron
meteorites which contain more than 16% Nickel. They do not
display a Widmanstatten Pattern.
-
Basalt - are volcanic rocks primarily composed of the
minerals olivine, pyroxene and feldspar. -
Bolide
- a very large meteor which is sometimes accompanied by
loud sonic booms. -
Breccia - Rock composed of sharp-angled fragments made up of
the same material and embedded in a fine-grained matrix.
-
Carbonaceous Chondrites -
meteorites which are rich in Carbon. They are thought to
represent the earliest formed material in our Solar System or
even have cometary origin. -
Chondrites - (kon-drites)
meteorites which contain Chondrules. Chondrites
are primitive aggregates of early Solar System materials. -
Chondrules -
are small spherical rocks usually less than 1mm in diameter which formed
from molten or partly molten droplets while floating around in
space. Chondrites are composed primarily of these
materials. (see above)
Click Here for excellent examples of
chondrules. -
Class
/ Classification - is a meteorites scientific designation
into a particular type of specimen. (E.g. L6, EH5, Howardite,
CO3.6, IIAB, etc) -
Comet
- a body which orbits the sun and is primarily composed of
frozen water, ammonia, methane, carbon dioxide and many pieces
of rock and dust. Their distinct tail occurs when they approach
the sun from their suspected origin in the outer edges of our
Solar System. -
Crater
- formed from the collision of a large natural body from space
when it impacts a large body's (eg. planets, moons, asteroids) surface at high velocity.
-
Electrophonic Sounds - often associated
with the fall of meteorites comes unusual sounds which
can be like whistling, hissing, whizzing etc.
(See here for more information.) -
Enstatite - the pyroxene silicate
highest in magnesium content and a particular Classification
of meteorite.
-
Fall - a meteorite which was
witnessed to fall to Earth's surface. -
Falling Star - see Meteor. -
Feldspar - a mineral group of
silicate minerals commonly containing calcium, sodium,
potassium and aluminium. -
Find - a meteorite which has been
found and has no record of being witnessed to fall to Earth's
surface. -
Fireball - a
very large and bright meteor which can also often leave a
smoke trail. -
Fusion Crust
- in the last couple of seconds of luminous flight, the molten
surface of a meteor solidifies to form a thin, usually
black 'fusion crust'.
-
H-Chondrite -
ordinary chondrite with 'High Iron'. (About 12% - 21%
Metallic Iron) -
Howardite - an
Achondrite made of fragments of other types, usually
Eucrite, Diogenite, Mesosiderite and
chondrite. Howardites are broken meteoritic soils from the
surface of an asteroid.
-
Impact Melt - these
meteorites have formed from material that was liquefied or
partially liquefied from
the extreme pressure and heat generated by a large meteorite
or asteroid impact in space. -
Igneous Rock
- rock produced directly or indirectly from the solidification
of molten magma (lava). -
Inclusion -
a body of material enclosed by a different material. -
Individual -
a whole unbroken or uncut meteorite specimen. -
Interstellar
Dust - small particles which originate outside of our Solar
System. -
Iron Meteorite
(Irons) - meteorites composed mainly of iron and
nickel. -
Iron Shale -
see Shale.
-
L-Chondrite -
ordinary chondrite with 'Low Iron'. (About 5% - 10%
Metallic Iron) -
LL-Chondrite -
ordinary chondrite with 'Low total Iron, Low
Metallic Iron.
(About 2% - 3% Metallic Iron)
-
Matrix - the embedding medium between chondrules,
metallic iron grains etc.
-
Metachondrite - term used to describe a Metamorphosed
Chondrite. They are texturally evolved rocks from Chondritic
precursors and also known as Primitive Achondrites.
-
Metallic Iron - is iron in its metallic form. Irons
and Stony/Iron Meteorites are primarily made up of
metallic iron in the form of two main minerals. (See
Kamacite & Taenite)
-
Meteoroid - is a small piece of dust, rock, ice or metal moving through space. They
range in size from a speck of dust but are smaller than an
asteroid.
-
Meteor
- is a meteoroid that has entered the Earths atmosphere and
burns brightly leaving a flaming tail and sometimes smoke. They
are more commonly called 'Shooting Stars' or 'Falling Stars'.
Most meteors will burn up completely in the atmosphere.
-
Meteorite - is a meteor that has survived entry through the
atmosphere and reached the Earths surface.
-
Meteoritics - the study and/or science of meteorites
and associated phenomena.
-
Mesosiderite
- meteorites usually composed relatively evenly of iron/nickel and stony
material.
-
Minerals -
are naturally occurring substances which have a definite
chemical composition and a characteristic crystalline structure,
colour, and hardness.
-
Monomict - A mixing of the same textures and compositions.
(Eg. L6 with L6)
-
Octahedrite - Iron meteorite displaying a
Widmanstatten Pattern.
-
Olivine - is
a group of mainly iron and magnesium bearing silicate
minerals. See also Silicates.
-
Ordinary
Chondrite - these are the most common meteorites
found. This term encompasses meteorites belonging to the
H-Chondrite, L-Chondrite or LL-Chondrite
group.
-
Oriented
(meteorite) - a meteorite often displaying a conical
shape which has resulted from very stable flight through Earth's
atmosphere and thus undergone even ablation.
(See
here for more detail)
-
Pallasite -
Stony/Iron meteorites
usually composed of olivine crystals set in a matrix of
metallic iron.
-
Parent
Body - a larger body from which a meteorite is thought
to originate. (See
here for more detail)
-
Plessite - is not a mineral as such but rather a fine grained mixture of Kamacite and
Taenite.
-
Polymict - A mixing of different
textures but the same compositions (Eg. L5 light
with L6 dark)
-
Primitive
Achondrite - a meteorite whose bulk composition is
approximately chondritic, but has been texturally modified by
partial melting or metamorphic recrystallisation. - NAU
-
Pyroxene - a group of rock forming
silicates commonly containing iron, magnesium, calcium,
aluminium and sodium.
-
Regmaglypts - are thumbprint-like
depressions on a meteorite caused by the uneven flow of
air during passage through the atmosphere and the consequent
surface melting and ablation.
-
Regolith - Mixing of
different compositions and/or petrologic stages with a
fine matrix at the surface of an asteroid, or moon, etc.
Measurement of solar
radiation is involved to show surface exposure implying multiple
events at
surface. (Eg. H3-6)
-
Shale - the product of complete alteration of iron
meteorites to iron oxides by weathering on Earth. -
Shooting Star
- see Meteor. -
Silicates / Silicate Minerals - Group containing a large
number of common rock forming minerals, that consist of
repetitive SiO4 groupings combined with one or more
metals and sometimes hydrogen. -
SNC
- acronym term used for Mars meteorites. (S-Shergottite,
N-Nahklite,
C-Chassiginite) -
Stony
/ Stones (meteorites) - meteorites composed
predominantly of silicate minerals. -
Stony/Iron (meteorites) - meteorites composed of
iron-nickel metal (metallic iron) and silicate
minerals in roughly equal proportions. -
Strewn
field - the usually elliptical area over which fragments
from a shower of meteorites are distributed on the
ground.
-
Taenite - is an iron-nickel mineral high in nickel content. (More
than 25%) -
Tektite - naturally occurring and once airborne glass
ejected by explosive meteorite impact. -
Thumbprints - see Regmaglypts. -
Troilite - is Iron Sulphide (FeS). Commonly occurring metallic
mineral in most meteorites which is a dull yellow or
brass-like colour.
-
Unclassified - the term given to meteorites
which have not been officially examined, classified and named. -
Ungrouped - meteorites which do not fit into any existing
classification. Once five different specimens have been found, a
new classification may be developed.
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