Tektites are made of opaque to translucent, green, brown, grey, yellow-grey or black glass. Moldavites are typically green, while Australites are usually black or dark brown.
Their chemical compositions are similar to both granite and impure sandstone (greywacke) or soils of these compositions, being high in silica (68-82%) with 10-14% alumina and lesser iron, magnesium, calcium, potassium and titanium. These components did not have time to combine and form crystals, but cooled quickly to form a glass.
Tektites do not contain any water. They can be mistaken for obsidian or pitchstone (black volcanic glasses), but these will emit some water on strong heating. With a hardness of 6-7 on Moh's scale, tektites will easily scratch window glass. They have a density range of 2.2 (Libyan glass) to 2.8 (Moldavites), but are usually 2.4 to 2.5 grams per cubic centimetre. This is a little lighter than quartz beach sand. Human built objects can be mistaken for tektites, particularly molten bottle glass, glass marbles, and black buttons. Many of these will not have the correctly-shaped rims, symmetrical structures or colours of real tektites, while others will be too heavy or too light.
Copyright © Australian Museum, 2004