Source: https://www.gia.edu/garnet-care-cleaning#:~:text=Warm%20soapy%20water%20is%20always,Steam%20cleaning%20is%20not%20recommended.
Hardness and toughness
Gem and mineral hardness is measured on the Mohs scale. The numbers are based on the relative ease or difficulty with which one mineral can be scratched by another. But the Mohs scale is deceptive. The steps between the minerals are not evenly spaced. For example, diamond is only one number away, but it’s many times harder than gems in the corundum family.
Depending on type, garnet hardness ranges from 6.5 to 7.5 on the Mohs scale. For example, almandine, pyrope, spessartine, and tsavorite are on the harder side while demantoid is a bit softer.
Garnets have fair to good toughness, making them durable enough for all jewelry styles as long as they are treated with the proper care. Garnets should not be subjected to any hard blows or rough wear.
Stability
Garnets are stable to light and chemicals. They can be attacked by hydrofluoric acid.
Cleaning
Warm soapy water is always safe for cleaning garnets. The ultrasonic cleaner is usually safe except for stones that have fractures. Steam cleaning is not recommended.
Treatment and durability considerations:
Garnets might rarely be treated by fracture filling. Only warm soapy water should be used to clean fracture-filled stones.