"To anyone who has worked with
them, tektites are probably the most frustrating stones ever found on
Henry Faul, 1966.
Faul’s description of tektites still holds true
even today. While more data has
been collected and theories on the origin of tektites have been reduced,
these small, glassy objects still provide many questions for current tektite researchers. Let us
begin our discussion with a brief history lesson.
The name tektite is derived from the Greek tektos,
or melted. These glassy objects have fascinated people of the world for
centuries. The first known description of tektites comes from China around
900 B.C., during the T’ang dynasty, in a book by Liu Sun, Ling Piao
Lu Yi, loosely translated as “Notes on the Wonders Beyond the Nanling
Mountains in Kwangtung”. Liu Sun stated that lei-gong-mo, or
inkstones of the Thundergods, black stones that made a ringing sound when
struck and possessed a brilliant luster, were collected after rainstorms.
Barnes (1973) Until the late 19th and early 20th century,
tektites remained an enigma. Little research was conducted until Alfred
Lacroix, a researcher from the Musee National d'Histoire Naturelle, Paris,
described a large tektite deposit in Indonesia, and later identified the
Ivory Coast as another tektite locality. Barnes (1973) These discoveries,
and the subsequent publishing of the research about them sparked the
interest of other scientists throughout the world. The remaining
first-half of the
20th century was spent locating and identifying additional tektites and
their localities across the globe. As more and more tektite localities
were found, many different hypotheses were developed to explain
the unique chemical and physical properties of tektites. During the
1950’s and 60’s, tektite research came to the forefront because of the
belief that they might have originated from the Moon. This theory was
later discounted by most scientists, but the vast body of information collected during this
period provided the basis for the tektite research that still continues
What is a tektite?
Tektites are rounded, pitted bodies of silicate glass,
nonvolcanic in origin, most likely derived by large hypervelocity
meteorite collisions with terrestrial rocks. Commonly about the size of a
walnut, tektites can vary from sand grain sized microtektites,
weighing grams, to large, blocky, Muong Nong-type specimens weighing up to
12.8 kg (28 pounds). Tektites can differ in both color and
age, depending on where they are found. Commonly black color,
tektites can also vary from light green to greenish yellow. Ages vary from
~35.5 million to ~750,000 years old. Chemically, tektites are uniquely
characterized by extremely high silica contents ranging from ~70% in
Australasian tektites to ~98% in Libyan Desert Glass.
|| Most current scientists theorize that tektites are formed by the rapid
heating and subsequent cooling of quartz-rich soils and rocks. The impact
of large meteorites with the surface of the Earth provides enough energy
to melt soils and rocks and disperse the molten ejecta of these impacts
great distances, forming tektites. Mixtures of shale and quartz sandstone
or certain igneous rocks, possess similar compositions to that of the
tektites, leading researchers to believe that these rocks may be the
“parent” or “source” rock of tektites. Additionally, terrestrial soils,
which cover almost the entire globe, have been found to also possess the
proper chemical compositions, to create tektites. Produced by the erosion
of many different source rocks, these soils would be a potential source of
tektite-melt material. Before we begin discussing in depth the process of
tektite formation, perhaps we should consider why the meteorite impact
theory has gained favor with modern-day researchers.
(Click on images to enlarge.)
Ablation vs. Abrasion
Ablation is the removal and reshaping of molten surface
layers of meteorites and tektites by vaporization during flight through
the Earth's atmosphere.
Abrasion is the mechanical wearing or grinding away of
rock surfaces by the friction and impact of rock particles transported by
wind, ice, waves, running water, or gravity.
Bates and Jackson (1984)
With tektites closely resembling obsidian, many early researchers believed that they were indeed
products of terrestrial volcanic eruptions. Their various shapes were
theorized to result from abrasion by wind-blown sand or shaping by water.
Chemical properties and the subsequent determination that tektite surfaces were ablated NOT abraded, later
disproved this theory. (Obsidian is found in nature as a black glass, a
product of the ash trapped within the crystal, the presence of the green
and yellowish-green moldavites and Libyan Glass, as seen below, provides
an easy example of why this theory can be discounted.)
Many other theories were developed to try to explain
the existence of tektites, some of these included:
The suggestion that tektites were actually man-made objects, created during the smelting
process of ancient civilizations.
However, the chemical and physical
property of tektites, as well as the stratigraphic ages of their
localities completely discounts this theory. (Humans developed rudimentary
smelting techniques as early as 6000 B.C., however, the youngest tektite
are around 100,000 years old.)
What is a stratigraphic age?
The length of geologic time during which
the rocks of a particular type, differentiated by characteristic
properties and attributes, were deposited. These rock units are often used
to date materials within them, or that occur before or after the rock was
| The idea that natural fires such as forest fires or ground fires igniting coal seams
could be a source of tektites.
fires may reach very high temperatures, the presence of ablation shapes
unique chemical properties in tektites discounted this theory.
Another proposed alternative for tektite formation was the fusing of silica-rich
surface soil and dust by lightning.
These forms, called fulgurites, while
having attained high enough temperatures to have melted the silica, do not
have the same appearance as tektites, often occurring as soda-straw shaped
tubes, as seen here, and possess none of the unique chemical and physical
properties that set tektites apart from other naturally occurring glasses.
In addition, the nature and scale of tektite occurrence discounts this
theory as well. Lightning strikes occur thousands of times each day. If
this theory held true, tektites would be found throughout the world, in
Theories suggesting that tektites were material
ejected from lunar volcanoes or that tektites were formed by the impact of
meteorites with the Moon gained wide acceptance during the 1950's and
60's. However, some scientists doubted these theories, suggesting that
tektites were actually formed on Earth by meteorite and/or comet impacts.
After the Apollo Moon landings scientists studied and compared the
chemical composition of lunar rocks to tektites. Their conclusions showed
that there was little to no similarity between tektites and lunar
materials, shedding doubt on the lunar origin of tektites, and adding
credit to the terrestrial impact theory that is now widely accepted.
The main issues facing
both past and current scientists working with tektites is the determination of when, where, and
how they originated. To deduce the conditions necessary to produce tektites, it is
important to recognize several significant properties about tektites. These properties include;
- Distribution and geological age.
- Physical properties and chemical compositions.
- Shape and melting features of some specimens.
- Internal features.
Tektites are distributed across the Earth in areas
called strewnfields. These strewnfields are found on every continent
except Antarctica. The main strewnfields found on Earth
are the Australasian, the largest of all of the strewnfields,
covering an estimated 10% of the Earth’s surface, the Ivory Coast,
Czechoslovakian, and North American strewnfield.
varieties are given distinctive names; derived from the region of their
strewnfield occurrence, and/or the place or country in which they are
found. Examples of regional nomenclature include “moldavites”, named for
the Moldau River in the Czech Republic, and “bediasites”, named for the Bedias
Indians, for those found in Texas.
Others, named after the region
or country in which they are found, include australites, javanites,
indochinites, and philippinites. A few groups, such as the Ivory Coast
tektites and Georgia tektites, are not specifically
Area of Occurrence
Possible Source Craters
Australia, Tasmania, Indonesia and
Ries Crater, Germany
Ivory Coast of Africa
Botsumtwi Crater, Ghana
Texas, Georgia, Martha’s Vineyard,
Chesapeake Bay Crater, U.S.A
(Images and information
about the possible source craters of tektites)
What is a strewnfield?
strewnfield, is commonly used to describe a finite area
across the globe in which specific materials, in our case, tektites, have
fallen. The boundaries of the strewnfield are confined by the extent of
the material. Each strewn-field is comprised of specimens similar in age
and chemical compositions, including tektites found on land, as well as
microtektites, found in deep sea sediments, and are inferred to have been
created by impact event of the same age.
(Map of major
What are the varieties of tektites?
- Darwin Glass
- Georgia Tektites
- Ivory Coast Tektites
- Libyan Desert Glass
- Martha's Vineyard Tektite
The ages of tektites are derived by several means.
The first and most direct way of dating a tektite is by measuring the
solidification age of the glass through the use of 87Rb/87Sr
decay measurements. The age of ablation caused by atmospheric entry or
re-entry can be derived by potassium-argon decay measurements. Fission track analysis,
another geochronologic tool, can indicate the latest heating episode of the
tektite glass . Finally, the stratigraphic age of sediments
surrounding tektites can provide a general time frame of formation and/or
deposition of the tektites.
Tektites range in age
from 35.5 million to 750,000 years old. Using these dates scientists have
tried to correlate the ages of tektite strewnfields with impact craters
across the globe. For the most part, these researchers have been
successful in determining the source craters for tektites, however, the
source crater for the Australasian strewnfield, still has not been found,
allowing some people to still question the meteorite impact theory.
An explanation of the ideas and methods
behind radiometric dating and fission track analysis, both topics in the
broad subject of geochronology, can be a little hard to understand,
with entire semesters dedicated to learning the subject matter. If you
would like more information on these subjects please click the links
Radiometric dating and fission track analysis
of a bediasite.
| Physical properties and chemical composition set tektites apart from other
naturally occurring glasses.
Normally the first thing mentioned about tektites is
their color. Outwardly, tektites appear to be glossy-black, but thin sections of
specimens are translucent, and generally appear to be yellowish brown. The
black color of most tektites can vary, however, depending on the
strewnfield the tektite is located in. Moldavites are dark green and
Libyan Desert glass is greenish-yellow to straw yellow in color.
Tektites possess a hardness of between 6 and 7 on the Mohs' scale.
What is hardness?
Hardness is a measurement that determines an objects resistance to
scratching. Hardness is measured using the Mohs’ Scale, with values
ranging from 1 (talc) to 10 (diamond), where a substance with a lower
value will be scratched by an object possessing a higher hardness value.
Here are the hardness values of some common objects:
· Fingernail = 2.5
· Copper Penny = 3
· Knife Blade = 5.5
· Glass = 5.5
· Steel File = 6.5
||% composition (range)
0.00 - 3.76
|| As seen on the table to the left, silica is the most common chemical
constituent of tektites. Silica content, is often measured by using two
physical characteristics, refractive index and specific gravity. Percent
silica composition ranges from around 68% in Ivory Coast tektites and
Philippinites to around 98% in Libyan Desert glass. It is believed that
variations in the silica content of tektites is due to the silica content
of the parent rocks. It must be noted that some types of obsidian also
possesses high silica contents, up to ~80%, however, there are several
other features of tektites that set them apart from other forms of
naturally occurring glasses.
What is refractive index?
A technique used to measure the deflection of light as
it passes from one medium, normally air, into another medium of differing
density. Tektites normally possess refractive index ranges between 1.4600
What is specific gravity?
A measurement used to
determine the density of an object by finding the ratio of the weight of a
given volume of substance to the weight of a volume of water displaced by
the object being measured. Tektites have specific gravity ranges between
2.275 and 2.510.
The Relation of Specific Gravity and Refractive
Index to Silica Content.
Specific gravity, and
refractive index show an inverse relationship to silica; that is, the
higher the refractive index and specific gravity, the lower the silica
|| Often included within tektites are tiny particles of lechatelierite. The
presence of these particles is important because obsidian and other
volcanic glasses do not contain these particles. Air bubbles are often
associated with lechatelierite. These associated bubbles are indicative of
the temperature at which the lechatelierite formed.
||What is lechatelierite?
Lechatelierite is a very rare, fused silica glass, formed by the melting
of quartz crystals by extremely high temperatures and pressures. When
associated with tektites, this material is normally used as evidence for
shock metamorphism, caused by a meteorite impact event.
What does the presence of lechatelierite within
The presence of lechatelierite indicates that
tektites were formed by the melting of quartz-bearing
minerals, and that the temperatures reached during the melting of the
parent rock was in excess of the melting point of quartz. (< ~900º C)
Quartz-bearing materials on Earth include terrigenous sedimentary rocks,
acid igneous rocks and soils formed by quartz-bearing rocks. Barnes (1940)
Bubbles associated to lechatelierite: What they
When lechatelierite is formed by the
melting of quartz, the gas and liquid filled inclusions found within
crystals are volatilized. These volatilized materials are normally lost at
very high temperatures, thereby leaving the tektite with no bubbles. The
presence of bubbles indicates that temperatures were intermediate. Lower
temperatures lead to “frothy” lechatelierite, where the volatilized
materials within the crystal expanded, but did not coalesce into bubbles.
|| Other bubbles, not related to lechatelierite particles, are also found in
tektites. These bubbles are formed by gases that were trapped while the
tektite material was molten. Variations in shape and gas content of these
bubbles can tell us about the conditions present during tektite formation.
However, these bubbles can also lead to errors in specific gravity
measurements. Therefore, refractive index is normally seen as the most
accurate way to measure silica content.
What do air bubbles tell us about the tektite?
The abundance, size and shape of
bubbles distributed throughout tektite glass are important factors in
determining the history of the glass. As a melt becomes hotter it becomes
more fluid and more of the vaporization products escape, resulting in the
retention of fewer and smaller bubbles. Also, the hotter the fluid, the
more likely that the bubbles will be spherical. Irregular bubbles indicate
that the melt did not become sufficiently fluid for surface tension to
draw the bubbles into spheres; elliptical bubbles indicate that the melt
flowed as it cooled.
In addition to their distribution, age, and physical and chemical properties,
tektites may be subdivided into three distinct
types on the basis of their external form.
(click here to see a thin section of a Type A tektite)
Also known as the Muong Nong-type,
these tektites are often chunky or platy in external form, but often show
evidence of internal compositional layering as well as variations in
bubble content. Believed to be formed by puddles of molten glass, this
tektite type was discovered in 1935 by Lacroix, they are named for the
town of Muong Nong, Laos, located near where they were first found.
||What is compositional
Or “splash-form” tektites,
consisting of specimens, when unbroken, can be shaped as spheres,
ellipsoids, rods, teardrops, dumbbells, and boats. Some of these tektites
show contoured, bent and rolled internal structures due to fluid flow
while molten. The shapes of splash-form tektites have previously been
erroneously associated with aerodynamic shaping. In actuality, these
tektites were shaped by variations in rotation rates of partially melted
glass droplets. With dumbbell shaped specimens
showing the highest rates of rotation and spheroid specimens exhibiting
little to no rotation. The size of these “splash-form” tektites is limited
by the surface tension of the melt from which they are formed.
These tektites are type B forms
that have been subjected to attack by heat on one side (Called the
anterior side), so that a portion of the mass has been lost to ablation
and/or has been resculpted to form a flange derived from the anterior
side’s material. Often known as flanged “buttons”, these forms are most
common in Australites, but are also found in some Javanites.