Aussie Lapidary Forum

Gemstones & Jewellery => Gemstone Discussions => Topic started by: harryopal on January 16, 2019, 07:43:40 PM

Title: Any geologists out there?
Post by: harryopal on January 16, 2019, 07:43:40 PM
I wonder if there are any geologist followers of this website? The reason I ask relates to a post I just made "Areas around Colac" and remarking on the lovely specimen volcanic, olivine bombs sprinkled with peridot that used to be found (maybe still found) at Mt Shadwell.


I am now living in Bali where Mt Agung keeps venting every now and then which makes me wonder if it is reasonable to suppose that one might find similar volcanic bombs around the flanks of Mt Agung? Are olivine bombs a feature of all erupting volcanoes or does it require a particular type of geological formation.?
Title: Re: Any geologists out there?
Post by: MakkyBrown on January 16, 2019, 08:16:53 PM
I wonder if there are any geologist followers of this website? The reason I ask relates to a post I just made "Areas around Colac" and remarking on the lovely specimen volcanic, olivine bombs sprinkled with peridot that used to be found (maybe still found) at Mt Shadwell.


I am now living in Bali where Mt Agung keeps venting every now and then which makes me wonder if it is reasonable to suppose that one might find similar volcanic bombs around the flanks of Mt Agung? Are olivine bombs a feature of all erupting volcanoes or does it require a particular type of geological formation.?
I remember reading somewhere it was raining olivine. Think this might have been from a fairly recent eruption, just googled :)

https://www.popularmechanics.com/science/environment/a21527670/kilauea-hawaii-volcano-crystals-olivine-green/
Title: Re: Any geologists out there?
Post by: Blash on January 17, 2019, 11:06:56 PM
Hi Harryopal, just a quick spot of research on this one, I doubt that you would find olivine bombs near Mt Agung the chemistry isn't quite right. You would typically only see olivine bombs in mafic to ultramafic rocks whereas Mt Agung appears to be more of an Intermediary composition.
Title: Re: Any geologists out there?
Post by: harryopal on January 18, 2019, 12:09:53 PM
Thank you Blash. I also got the following information from Peter Rendevouz on Facebook. you'd have greater success looking in hawaii .. there is no olavine bombs as you call them at Agung. Olivine is made up primarily of magnesium, iron, silicon, and oxygen, and the combination of the latter three creates a class of mineral known as an iron silicate. It doesn't come raining from the sky or eruptions.... it can be found in old lava having formed after ejection.