Igneous Rocks
Sites I visited to explore this topic:
Vesuvius, Marina Grande, Marina Piccola, Villa Comunale
Igneous Rock Mineralogy
There are two types of Igneous rocks: intrusive and extrusive.
Basalt is mafic and extrusive. Rocks containing olivine and pyroxene are typically mafic.
Rhyolite is felsic and extrusive. Rocks containing quartz, potassium feldspar are typical felsic.
Plagioclase can be found in both mafic and felsic rocks and the presence of amphibole indicates more of an intermediate composition.
Rocks with a high silica content will be lighter. Rocks with less silica and more iron and magnesium will be darker in color.
Rocks containing large visible crystals (phenocrysts) embedded in a finer-grained matrix are indicative of a complex cooling history. This history might be where the large mineral cooled slowly and then the rest of the magma around it cooled more rapidly.
Scoria vs. Pumice
SIMILARITIES: porous volcanic rocks with vesicular texture
DIFFERENCES: magma composition, color and density
SCORIA: dark in color (reds, blacks, browns), larger vesicles, denser (sinks), form from basaltic magmas rich in iron and magnesium
PUMICE: light in color (white, grey), more abundant and smaller vesicles, less dense (usually floats), form from rhyolitic magmas rich in silica
Sorrento Cliffs and Tufa Rock
The Sorrento cliffs were made from ash deposits from the Ignimbrite Campanian eruption 39,000 years ago. That eruption is the highest energy eruption known in the Mediterranean region.
Tufa rock is a porous, sedimentary rock primarily composed of calcium carbonate (CaCO3), formed by the precipitation of minerals from water.
Tuff can be defined as a volcanic conglomerate. The Neapolitan yellow tuff (NYT) is from a major volcanic event in the Phlegrean fields around 15,000 years ago.
The minerals in NYT can vary, but Limonite is the main reason for it's yellow coloration. Limonite is a combination of multiple hydrated iron oxide minerals (primarily Goethite).
