12.79g DARWIN GLASS - Impactite
On Offer: 12.79 gram Darwin Glass
Fragments of Darwin glass are found scattered over a 410 km² (160 miles squared) area. Such an area is called a strewn field. On slopes and flat ground between 250 and 500 m elevation, the glass occurs with quartzite fragments buried under peat and soil. The peat is normally around 20 cm thick, and the quartzite fragment horizon is typically 30 cm thick. On mountain peaks higher than 500 m, the bedrock is directly exposed to the air, and Darwin glass occurs occasionally on the surface. In valleys below 220 m the Darwin glass is buried below peat and sediments. The glass occurs north, west and south from the crater. Its distribution extends to Kelly Basin and the lower northeast shore of Macquarie Harbour. Northwards it extends almost to the Lyell Highway and Crotty Dam. Darwin glass is rare in the crater itself.
The glass is light to dark green, white or black. The glass takes the form of twisted masses, fragments or chunks up to 10 cm. Internally it has a flowing texture defined by lines of elliptical bubbles. There are two kinds of Darwin glass when composition is measured. The dark glass is also enriched in chromium, nickel and cobalt. A possible explanation for the chemical differences is that, in addition to being mainly composed of melted local metamorphic rocks, the type 2 glass also contains a component of extraterrestrial material from the meteorite. Darwin glass has been dated at about 816,000 years old using argon dating methods.
The glass is an impactite resulting from the melting and rapid quenching and vitrification of the local rocks due to the impact of a large meteorite. The assumed source is a 1.2-kilometer-wide topographic depression known as Darwin Crater. The crater is filled with 230 m of sediments and breccia. A crater of that size would be created by a meteorite 20 to 50 meters in diameter and its impact with Earth would release 20 megatons of energy.