Tektites is a mineral with a hardness of 5 out of 10 on the Mohs scale of mineral hardness [?]. These Amorphously structured gems are made of silicon dioxide, their full chemical compound being SiO2.
Tektites are glass specimens rich in silica that many believed were actually meteorites. But, the locations in which tektites have been found, and their chemistry, led scientists to suggest that they may not in fact have come from outside planet Earth. Another conjecture is that tektites are formed from rocks that melted after being hit by a meteorite. Tektites actually have a composition not unlike that of some volcanic rocks. These rocks have a high silica content, and are also rich in oxides of potassium, calcium, and aluminum.
The tektite rocks are small in size, usually about 200-300g (7-10 oz) in weight, and have a disc or egg-shape. They may have either a smooth or rough surface, which can also be a a bit gravelly or scarred. Their color is usually green to black, and rarely yellowish.
But to gemologists, the most interesting specimens of tektites are not those that are metallic or stony that fall from the sky, but the glass-like tektite rich in silica, are very similar to the volcanic glass obsidian, yet unlike them, have no water content.
These appear as small, rounded, pitted grains that are not produced by volcanic activity. The lechatelierite in tektites suggest shock metamorphic activity created by meteoric impact. This is the kind of material that is also formed when quartz sand is melted by a lightning strike.
These bottle-green glassy tektites were found in the late 1700s in western Moravia and near the Bohemian river Moldau, with the Czech name Vltava. The pieces were named for the river location and called moldavites. They are still thought to be formed from meteoric impact, even as suggested by its appearance, like a bouquet of leaves frozen in mid-splash. They may be transparent green, greenish brown or brown in colour.
These lumps of glass, often fissured on the surface - may also evoke the shapes of alpine mountain ranges, with craggy peaks, or have rounded crests with a surface that is bubbly or looks like a cluster of grapes.
Aside from moldavite, other varieties of tektite include: bediasite, australite (button-shaped), billitonite, javaite, Libyan desert, and Darwin glass.
Czech moldavites fall into three categories. Oval or spherical specimens are pale or bottle-green with few included bubbles and less obviously flattened. These are silica-rich and alumina-poor with little lechatelierite content.
Moldavites from most other southern Bohemian finds are bottle-green, more flattened and with profuse bubbles. Their lechatelierite content is higher.
Moravian specimens have fewer bubbles and are shaped liked spheres. Some are found in Upper Miocene sediments and others in Pliocene and Pleistocene sediments. The rest are found in slope lavas and alluvial areas with Pleistocene material. As is usual with continuously-mined areas, the Czech mines are close to running out of moldavites.
Button-shaped glass pieces (australites) have been found in South Australia and Tasmania. The variety billitonite was found on Billiton Island between Sumatra and Borneo, and specimens tend to be dark brown.
Colombia produces colourless tektites that are also button-shaped. The Jukes-Darwin field near Queenstown, Tasmania, produces silica-rich and alumina-poor colorless to olive-green to black specimens and are called darwinite or queenstownite.
Tektite is also named as obsidianite and spelled as "tectite."
Tektite derives from the Greek word "tektos", meaning "to melt." Since tektites were formerly thought to be non-crystalline meteorites, they used to be called "glassy meteorites."
Notwithstanding the continuous argument over where tektites really come from, the dominant explanation today is that they result from the melting of Earth-based rocks on the impact of a meteorite. Even more unlikely is the old proposal that tektites were propelled towards our planet from a large volcano on the Moon. From what is known of its composition, tektites condensed from vaporized materials which were formed as a result of the high velocity with which huge meteorites collided with the Earth. These materials then developed drip-like forms with a glassy, amorphous texture. Supporting that conclusion is the fact that tektites are found in the "strewn fields" of meteoric craters.
Tektites are usually named after a particular occurrence, e.g. Moldavite (Moldau, Czechoslovakia), Australite (Australia), Georgiaite (Georgia, USA).
Tektites are used as faceted gems and cut cabochon usually from the bottle-green moldavite varieties. The material has been cut as gemstones producing green stones. Cut moldavite has been sold under a variety of fancy and completely misleading names, such as "bottle stone", "obsidian", "water chrysolite" and "pseudo-chrysolite". The stone has also been known under the name bouteillenstein.