One of the most important tests for identifying mineral specimens is the Mohs Hardness Test. This test compares the resistance of a mineral to being scratched by ten reference minerals known as the Mohs Hardness Scale.

Mount Etna of Italy is thought to be the world's oldest active volcano. The first record of its eruption dates back to 1500 BC. Since then, Etna has erupted 190 times.

The core of the Earth is primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.

The slip rate along the fault ranges from 20 to 35 mm (0.79 to 1.38 in)/yr. At this rate, Los Angeles and San Francisco will be neighbors in about 24 million years.

Volcanic ash and weathered basalt produce some of the most fertile soil in the world, rich in nutrients such as iron, magnesium, potassium, calcium, and phosphorus.

Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools rapidly with minimal crystal growth.

The San Andreas Fault is a continental transform fault, meaning the plates slide past each other along a fault line. It extends roughly 800 miles (1,300 km) through California and forms the tectonic boundary between the Pacific Plate and the North American Plate.