Tektite

TEKTITE, the name given by F. E. Suess to the glass bodies occurring isolated on the surface or in gravels, in Moravia and Bohemia, where they are called moldavites, the East Indies, where they are known as billitonites, and Australia, there known under the name of australites and obsidianites (from Gr. melted). In Tasmania, an exceptional type is met with in the Mt. Darwin region on the west coast ; these glass bodies are known as Darwin glass (or queenstownite). Isolated types of tektites have also been seen in Sweden and Colombia (South America).

In the Moldau district of Bohemia the moldavites occur as flat, rounded or ellipsoidal bodies of a bottle-green colour, and usually with a pitted or corrugated surface. The homes of these tektites are river gravels or deposits of late Tertiary or Recent age. The colour of this material led to its being commonly called Bouteillenstein. Australites are found distributed over wide areas remote from volcanic regions in Australia, principally in Victoria and the central goldfields of Western Australia. They exhibit a great variety of curious forms suggestive of flight and rotation while in a molten or plastic state. These shapes are ellipsoidal, pear-shaped or button-like with a projecting rim like a saucer. They are darker and less transparent than moldavites. Billitonites

resemble australites more than moldavites, being dark like the former. They occur in river gravels in the island of Billiton, and are for the most part roughly spherical or ellipsoidal and possess glossy, deeply sculptured surfaces. Billitonites reach in size up to 3 in. in diameter and in weight to 16 ounces.

Composition.

While possessing the silica content of natural obsidians (7o-9o% the tektites contain a higher percentage of iron and magnesium, and excess of calcium and potassium over sodium. Nor do they contain, with one doubtful exception, signs of incipient crystallization as is common in obsidians. The dis tinctive chemical composition of these bodies is reflected in their specific gravity and light refraction, which enables them to be separated from rhyolite and trachyte obsidians. They have been claimed as originating by the fusion of dust in the air by light ning and that they are really fulgurites, but little can be said for this view. Though they are of widely different composition from the iron or ultrabasic meteorites, a meteoritic origin remains as the least objectionable of all theories.

Analyses of some typical tektites are given below.