Garnet as a hydrothermal mineral provides evidence for formation under which conditions?

• A. Great depth and high temperature
• B. Shallow and low temperature
• C. Surface weathering
• D. Low depth and low temperature

Answer: (A)

Garnet forms and remains stable in rocks that have experienced high temperatures and significant burial pressure. In hydrothermal systems, hot, mineral-rich fluids circulating at depth can crystallize garnet as they react with surrounding rocks. This makes garnet a strong indicator of formation under elevated temperature and considerable depth, rather than at the surface where temperatures are low. Near-surface conditions or surface weathering would not favor garnet crystallization, and low-depth, low-temperature settings simply don’t provide the environment garnet requires. So finding garnet in a hydrothermal context points to formation at great depth with high temperature.