The Beechworth Burke Museum
Geological specimen - Basalt (igneous-volcanic) containing Olivine, unknown
This particular geological specimen was found in Mount Franklin or Lalgambook in Djadjawurrung, located between Daylesford and Newstead, approximately ninety minutes drive from Melbourne. The mountain is an example of a breached scoria cone (a steep conical hill of loose pyroclastic fragments) which was created by a volcanic eruption about 470,000 years ago, a date which may indicate the age of this geological specimen. The volcanic eruptions of Mount Franklin were most likely witnessed by members of the Dja Dja Wurrung Aboriginal tribe, who referred to this country as the 'smoking grounds'. Mount Franklin and the surrounding area appears to have been a place of considerable religious significance to Aboriginal people, there is evidence which indicates that frequent large ceremonial gatherings took place in the area.
Basalt is the most common rock on Earth’s surface, more than 90% of all volcanic rock on Earth is basalt. Basalt is an aphanitic extrusive igneous rock formed from the rapid cooling of low-viscosity lava exposed at or very near the surface of a rocky planet or moon. Specimens are black in colour and weather to dark green or brown. Basalt is rich in iron and magnesium and is mainly composed of olivine, pyroxene, and plagioclase. Olivine is the name of a group of rock-forming silicate minerals with compositions ranging between Mg2SiO4 and Fe2SiO4. Unlike other minerals, Olivine has a very high crystallisation temperature which makes it the first of the minerals to crystallise from magma. As magma cools, the crystals begin to form and settle on the bottom of the lava and form basalts that are abnormally enriched in olivine in the lower part of lava flows. According to H. M. King (on geology.com) "Olivine is thought to be an important mineral in Earth's mantle. Its presence as a mantle mineral has been inferred by a change in the behaviour of seismic waves as they cross the boundary between Earth's crust and mantle".
Lava from Mount Franklin and other volcanoes in the area filled valleys and buried the gold bearing streams that became the renowned ‘deep leads’ of the gold mining era. In 1852, as part of the Victorian gold rush, gold was discovered in the immediate area, this gold was created by lava flows during the Newer Volcanic period, which were mined intensively during the nineteenth century. Around 1865 the presence of a deep lead in Mount Franklin was established. Deep lead mining was initially unsuccessful, and it was not until the late 1870s that the Franklinford Gold Mining Company mined at Mount Franklin on a significant scale. A few years later the Mount Franklin Estate Gold Mining Company also struck gold, followed by the Shakespeare and Great Western companies in the mid-1880s. By the late 1880s, however, deep lead mining had ceased in the area.
Soon after gold was discovered in 1851, Victoria’s Governor La Trobe wrote to the Colonial Office in London, urging ‘the propriety of selecting and appointing as Mineral Surveyor for this Colony a gentleman possessed of the requisite qualifications and acquaintance with geological science and phenomena’. Alfred Selwyn was appointed geological surveyor in Australia in 1852 which began the Geological Survey of Victoria. In 1853-69 the Geological Survey issued under Selwyn's direction sixty-one geological maps and numerous reports; they were of such high standard that a writer in the Quarterly Journal of the Geological Society of London bracketed the survey with that of the United States of America as the best in the world. During his years spent in Australia, Selwyn collected numerous significant geological specimens, examples of which are held in collections such as the Burke Museum.This geological specimen is an example of basalt and olivine which shows the volcanic lava activity and geographical specific nature of Mt Franklin as a significant volcanic site. According to Agriculture Victoria 'The crater is one of the deepest in the Central Highlands area. It is a major megacryst site with some of the largest known Victorian examples of megacrysts of augite and an orthoclase. The small parasitic mound of Lady Franklin on the western flanks adds to the geological interest of the site'. This specimen also highlights the locality as a significant place for both indigenous activity and Victorian gold rush era mining practices.
This specimen is part of a larger collection of geological and mineral specimens collected from around Australia (and some parts of the world) and donated to the Burke Museum between 1868-1880. A large percentage of these specimens were collected in Victoria as part of the Geological Survey of Victoria that begun in 1852 (in response to the Gold Rush) to study and map the geology of Victoria. 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.An angular, solid hand-sized piece of grey volcanic Basalt with green/brown Olivine phenocrysts along one flat edge.Olivine in basalt / - label is probably
/ correct. / C. Willman / 15/4/21burke museum, beechworth, indigo shire, beechworth museum, geological, geological specimen, mineralogy, basalt, igneous rock, igneous-volcanic, volcanic geology, volcanic, olivine, olivine specimen, basaltoid
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The Beechworth Burke Museum