Pearl is a dramatic example of this, requiring high humidity lest it collapse. Never pack dessicant with pearl of any kind. The gem stone, opal an organic derivitive, is best stored in distilled water. Since the advent of the industrial revolution, high levels of sulphur dioxide pose a problem to the caretaker. In combination with oxygen and water it forms sulfuric acid.
Simple respiration produces carbon dioxide which in combination with water forms carbonic acid.
Both sulfuric and carbonic acids are powerful oxidants. Containers should be sealed and can even be flooded with inert gas to expel air. This is quite a cost effective way of atmospheric control for display and storage containers. A simple storage container can be constructed of large diameter PVC drainpipe capped at each end. Glued or screwed endcaps can be used that incorporate intake and exhaust valves suitable for flooding with inert gas.