Porphyry
Cobblestones under the microscope
01
These images originate from a rock called “rhyolitic ignimbrite”, from the Atesino volcano complex.
02
This is a product of a volcanic explosion that released magma that was especially rich in gas and silica.
03
When the volcano exploded, the hot ash and gas formed a cloud that descended down the slopes of the volcano at high speed, carbonising everything.
04
The solid component (ash) of these burning clouds consisted largely of crystals of volcanic minerals, including quartz and feldspar. These appear intensely coloured under the microscope.
| Name: | Riolitic Ignimbrite |
| Type of rock: | Pyroclastic rock |
| Minerals: |
Quartz, plagioclase, alkaline feldspar, biotite. Calcite, hematite, clay minerals as alteration minerals. |
| Fossils: : | absent |
| Location: | Lazise (n 45° 30′ 39.3″ E 010° 46′ 25.6″) |
|
Formation (deposit): : Formation (pebble): |
cobbestone of the glacial deposits of Sarca (morainic amphitheater of ): Atesino volcanic complex |
|
Era deposit: Era cobblestone: |
Pleistocene (less than a million years) Lower Permian (ca.300-270 million years) |
|
How the pebble was formed: How the rock was formed: |
: on the front of a lowland glacier. burning cloud (ash storm and volcanic gases at> 500 ° C) |
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