Weathering grade and shock stage

Do not confuse the scales

Both values supplement classification but are not simple quality scales. Their precise assignment follows petrographic criteria and should be taken from a robust classification.

Weathering begins after landing

Oxygen, water and salts oxidise metal and sulphides; silicates may stain or alter to clay minerals. Warm humid climates accelerate these processes, while cold deserts and Antarctic ice often preserve material longer.

For ordinary chondrites, grades W0 to W6 describe increasing terrestrial weathering from virtually fresh to strongly replaced. This is a petrographic assessment, not a precise clock: climate and storage prevent direct conversion into years.

Shock predates arrival on Earth

Shock is produced by collisions on the parent body. Pressure waves create fractures, planar features, deformation of olivine and pyroxene, transformation of feldspar and, at high intensity, melt pockets or dark melt veins.

A common scale for ordinary chondrites runs from S1 to S6. Shock and weathering are independent: a strongly shocked meteorite may be a fresh fall, while a weakly shocked find may be heavily weathered. Both must be recorded separately.