_Composition_: A natural glass, approximately 75% SiO₂, 15% Al₂O₃, 4%
FeO, also MgO, Na₂O, K₂O, and traces of other elements. _Crystal
structure_: amorphous. _Hardness_: 5 to 6. _Specific gravity_: 2.33 to
2.44. _Luster_: vitreous, often dull on weathered surfaces. _Color_:
dark brown, greenish brown, appears black in thick sections. _Streak_:
uncolored. _Cleavage_: none. _Fracture_: conchoidal. _Tenacity_:
brittle. _Diaphaneity_: transparent to subtransparent. _Refractive
index_: 1.488 to 1.512.
The average bediasite size is about 1 inch in diameter, although
specimens approximately 3 inches in diameter are known. The uncut
tektites are very interesting, showing a variety of shapes and surface
features (Pl. V, A) and many exhibit contorted flow structure. The
surface of many tektites is grooved or furrowed, while on others it is
smooth or frosted. The Texas tektites are known as “bediasites,” after
place names in Grimes County traceable to the Bedias Indians who
formerly lived there.
Dark brown and greenish-brown tektites have been found in Texas in
gravels at scattered localities in Walker, Grimes, Brazos, Burleson,
Lee, Fayette, Gonzales, Lavaca, and DeWitt counties. Outside of Texas
the only other authenticated tektite localities in the United States at
the present time are in Dodge and Irwin counties, Georgia. A fragment of
a similar tektite has recently been reported from near Martha’s
Vineyard, Massachusetts. The tektites reported from Oklahoma are now
known to be pebbles of obsidian.
Although tektites have little value or beauty as gemstones, they have
been cut by lapidaries as both faceted and cabochon stones. Tektites
take a high polish but are mostly so dark in color that they appear
black.
The origin of tektites is of great scientific interest and is currently
the subject of much debate. Some scientists believe that tektites are of
meteoritic origin, while others believe that tektites were formed by
various terrestrial processes. Since no one has actually observed a
tektite to fall or form, and many of the theories of origin are
difficult to prove without direct observation, the origin of tektites is
likely to remain in controversy for some time.