Gneiss: deformed pebbles
A stone with a mysterious history
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These images show a few mm of the thin section of a pebble collected at the base of the hills of Lake Garda.
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Desenzano and Peschiera are situated on these hills, made from strips of detritus left behind by the glacier during the Pleistocene era.
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Like a conveyor belt, the glacier gathered detritus from one wide part of the Alpine chain that is north of the lake.
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Our pebble was transported by the glacier; it is metamorphic rock, which has therefore been modified by high temperatures and pressure.
| Name: | Gneiss |
| Type of rock: | Metamorphic rock |
| Minerals: |
Quartz, plagioclase, muscovite, biotite, garnet, epidote, apatite, iron oxides. Chlorite, sericite, epidote, titanite as alteration
|
| Fossils: | Absent |
| Location: | Lazise (N 45° 30′ 39.3″ E 010° 46′ 25.6″) |
|
Formation (deposit): Formation (pebble): |
pebbles of the glacial deposits of the Sarca (morainic amphitheater of the Garda) unknown |
|
Age (deposit): Age (pebble): |
Pleistocene (less than a million years) unknown |
|
How the pebble was formed: How the rock was formed: |
on the front of a lowland glacier unknown |
Curiosity
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