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Silica, or silicon dioxide (SiO₂), is a fundamental chemical compound found in many types of rocks and minerals, particularly those associated with volcanic activity. In the context of magma composition and classification, silica content plays a crucial role in determining the physical properties of magma, such as viscosity, melting ...
Silica. Silicon dioxide, the most abundant rock-forming compound on Earth and the predominant molecular constituent of volcanic rocks and magmas. It tends to polymerize into molecular chains, increasing the viscosity of the magma.
The ease with which lava flows, and the structures it forms depend on how much silica and gas are in the lava. The more silica, the more polymerization (formation of long molecules) happens, stiffening the lava.
The high-temperature polymorphs after quartz — tridymite and cristobalite — have been identified in silica-rich volcanic rocks such as certain obsidians with a snowflake pattern of cristobalite...
Silica content (SiO2) is the most significant difference when discussing magmas and their viscosity. Some other differences which control the minerals (and therefore rock type) that form are the iron (Fe), magnesium (Mg), calcium (Ca), sodium (Na), and aluminum (Al) content as well.
Source: Volcano World http://volcano.oregonstate.edu/volcano-factoids Silica: Influences lava viscosity and overall shape of the volcano. Silica molecules form a strong bond that permits entrapment of volcanic gases and promotes explosive volcanic eruptions. Low-silican magmas allow rapid escape of gases and low-explosivity eruptions.
Figure \(\PageIndex{1}\): Micrograph of silica particle in volcanic ash. A cloud of these is capable of destroying an aircraft or automobile engine. Hot ash poses an immediate danger to people, animals, plants, machines, roads, and buildings located close to the eruption.