Historical information

This specimen was recovered from the Nigretta Falls (previously named the Upper Wannon Falls), Victoria. The falls are fed by the Wannon River that has its head waters in the Grampians mountains. Approx. 10km upstream of the Wannon Falls, Nigretta is a multi-channel segmented cascade of smaller drops and bounces guided by patterns of joints in a much older (Devonian) rhyolitic volcanic rock.
Both the Wannon and Nigretta Falls are iconic landscape features, entrenched in the history and identity of the region. These falls are particularly rare as they are the product of volcanic activity, which is unique in the context of the Volcanic Plain of Victoria. Waterfalls of this capacity are generally associated with the Uplands areas of Victoria, rather than the edges of the Volcanic Plain.

Significance

This specimen is part of larger collection of significant geological specimens in the Burke Museum that was collected from around the world between 1868-1880. A large percentage of these specimens were collection as part of the Geological Survey of Victoria 1852-1974. The Geological Survey of Victoria was an organisation founded in response to the Victorian gold rush to explore the geological and mineral resources and to record a detailed map of the state. It was headed by British geologist, Alfred Richard Cecil Selwyn (1824-1902), who was responsible for issuing over 60 geological maps during his 17 years as director. These maps were all hand-drawn and coloured and became the benchmark for accuracy for geological mapping. Collecting geological specimens was an important part of mapping and understanding the scientific makeup of the earth. Many of these specimens were sent to research and collecting organisations across Australia, including the Burke Museum, to educate and encourage further study.

Physical description

A solid, dark grey mineral specimen with pale terracotta coloured inclusions.

Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. Rhyodacites form from rapid cooling of lava relatively rich in silica and low in alkali metal oxides.

Inscriptions & markings

GEOLOGICAL SURVEY / R / S
55
FELSTONE PORPHY