Re: volcanic ashes

From: Carsten Troelsgaard (carsten.troelsgaard_at_mail.dk)
Date: 07/04/04 

Date: Sun, 4 Jul 2004 09:46:03 +0200

Hi Fred
Ups, I failed to answer this post in time, but I have a note anyway

"Frederik" <fd_news@hotmail.com> skrev i en meddelelse
news:b0999b8b.0407010310.35202f20@posting.google.com...
> Hello,
>
> One of the products of a volcanic eruption is volcanic ash, also known
> I believe as, volcanic dust. This volcanic dust consists out of glassy
> particles.
>
> I have 2 questions on this:
>
> Does every volcanic eruption produce these glassy particles?

There is glass, and there is glassy particles. A lavaflow is somewhat
glassy, that is, poorly developed crystallites. The particulate material is
associated to airborn pyroclastics.

> I.e. do
> all types of volcanic dust, as it is ejected from the erupting
> volcano, consist out of this glassy material?

volcanic bombs may theoretically contain wellgrown/'difficult to melt'
crystalls, but I don't know

>
> Do these glassy particles always contain potassium?

No. Potassium will be present if kalifeldspar is, and kalifeldspar is one of
the petrographic parameters ... which means, if a certain amount of
kalifeldspar is present the rock is said to have a a granittic/rhyolittic
composition. If not, the rockcomposition is basaltic but contains some fair
amounts of Ca, Na, Fe, Mg. The rhyolites tend to produce a lot of explosion
and ashes while basaltic flows are less viscous and just flow onto the
ground. You should give some margain to this information though.

>
> Thanks,
>
> Frederiek

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