Darwin Glass - Occurrence

Occurrence

Fragments of Darwin glass are found scattered over a 410 km² 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.

In controlled excavations of gravel deposits the abundance of Darwin glass was found to vary from 0.3 to 47 kg/m³. The highest abundance was found about 2 km from the crater, with the average abundance estimated at 3.4 kg/m³ of gravel over a 50 km² study area near the crater. From this it can be estimated that about 25000 tons of Darwin glass, or about 10000 m³, occurs in this 50 km² area. The amount of glass is large compared with the size of the crater. Preservation is helped by acid ground water which does not dissolve the glass, but this alone cannot explain the glass abundance. There is so much glass present that the glass must have been more copiously produced than in other meteorite impacts of similar size.