Lava Color vs. T emperature Approximate Color T emperature Slider T = 1000 °C
Temperature

A major control on the rates of most petrologic processes is temperature. Higher temperatures mean higher reaction rates, higher crystal growth rates, higher diffusion rates, etc. Why? What do higher temperatures do to rocks and minerals that speed things up? The temperature of an object is a meaure of the average kinetic energy of the movements or vibrations of atoms in that object. Temperature increases lead to increases in the motion of atoms and, therefore, increases in the internal energy of minerals and other materials.

Evidence for the motion of atoms in hot rocks includes the energy they emit as infrared radiation and, if hot enough, visible light. Very hot rocks and lava visibly glow during volcanic eruptions (see Figure 10 or watch some volcano videos).
Thermal Image of hot spring
The color of very hot rocks depends on temperature. Move the temperature slider in Figure 11 to see idealized color changes. What temperature is a red hot rock? Cooler, but still hot rocks and other materials "glow" in infrared wavelengths, invisible to our eyes but sensed as heat by our skin (see Figure 12 for an example). The energy radiated by rocks is a function of temperature, with hotter rocks radiating more energy than cold rocks.

Vibrational motions of atoms in minerals, even at low temperatures, seem at first to be at odds with those static, ball and stick crystal structure models often used in mineralogy courses. But the infrared and visible radiation of minerals at higher temperatures requires dynamic, rapidly moving atoms. Although we don't have a way to photograph those motions, it is possible to calculate what they might look like
Thermal Image of hot spring
and create movies of plausible motions based on theoretical models. Click on Figure 13 to see animations of atom movements in calcite at 300 K and at 1200 K. The scale of the movements at each temperature reflects the kinetic energy of the atoms at that temperature. Comparison of the atom movements at 300 K and 1200 K is consistent with the increased radiation of energy by minerals as temperature increases.

Although minerals are not gases, some aspects of the kinetic theory of gases can help us understand the effect of temperature on the rates of petrologic processes.