It forms when explosive stratovolcanoes
erupt and throw ash, debris,
other rock parts, lava, gases and steam into the air.
The fragments
solidify and later, are cemented together.
If it is hot
enough
they
are "welded" together,
forming welded tuff.
By R E M I B R I D O T via Flickr.com
If the mixture contains rhyolite,
rhyolite
tuff is formed.
By R E M I B R I D O T via Flickr.com
It contains biotite, feldspar,
quartz,
and
glassy, pumiceous fragments.
By R E M I B R I D O T via Flickr.com
If the mixture contains trachyte, trachyte
tuff forms.
By R E M I B R I D O T via Flickr.com
It contains mainly sanidine or anorthoclase, and lesser amounts of
feldspar, quartz, hornblende, augite and biotite.
By mlhradio via Flickr.com
If the mixture
contains andesite,
andesitic
tuff forms.
It contains quartz, chlorite, calcite,
chalcedony and epidote.
By only_point_five via Flickr.com Basaltic
tuffs form from basaltic
rock
material.
By only_point_five via Flickr.com
They are dark in
colour and vary in grain size.
By Ian Geoffrey Stimpson via Flickr.com
While andesitic and basaltic tuffs are
common, ultramafic
ones are very rare.
By Ian Geoffrey Stimpson via Flickr.com
They are associated with kimberlites - the rock
that contains diamonds.
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