Rhyolite typically crystallizes at temperatures ranging from 600 °C to 800 °C. This crystallization occurs as molten rock, or magma, cools and solidifies, forming the interlocking mineral grains characteristic of igneous rocks.
Understanding Rhyolite Crystallization
Rhyolite is an extrusive igneous rock, meaning it forms from volcanic eruptions at the Earth's surface. Its crystallization temperature is relatively low compared to other igneous rocks, primarily due to its high silica content.
Here's a comparison of rhyolite's properties, including its crystallization temperature, with another extrusive rock:
| Property | Komatiite | Rhyolite |
|---|---|---|
| Crystallization Temperature | > 1200 °C | 600 °C - 800 °C |
| Viscosity | Very Low | High |
| Major Other Elements | Mg, Fe, Al, Ca | Al, K, Na |
| Percentage SiO2 | < 40 wt. % | > 70 wt. % |
Key Characteristics Influencing Crystallization
Several factors influence the specific temperature range at which rhyolite crystallizes:
- Silica Content: Rhyolite is rich in silica, typically containing over 70 weight percent SiO2. High silica content increases magma viscosity and generally lowers its crystallization temperature.
- Mineral Composition: Rhyolite is composed predominantly of quartz and feldspar (orthoclase and plagioclase), with minor amounts of mafic minerals like biotite or hornblende. These minerals have crystallization points within the 600-800 °C range.
- Volatiles: The presence of dissolved volatile components (like water, carbon dioxide, and sulfur dioxide) in the magma can also affect the crystallization temperature, generally lowering it by reducing the melting point of the minerals.
- Pressure: While forming at the surface, the initial stages of crystallization can be influenced by pressure within the magma chamber prior to eruption.
Practical Insights
The high viscosity of rhyolitic magma, a direct consequence of its high silica content, affects its eruptive style. Unlike low-viscosity lavas that flow easily, rhyolitic lavas tend to be thick and pasty, often resulting in explosive eruptions or the formation of lava domes rather than extensive lava flows. The relatively low crystallization temperature means that these viscous magmas can cool and solidify more rapidly upon reaching the surface.
