Assign different custom fields to different categories

Hello guys,

I am currently developing a website for gemstone trade.
Every gemstone can be characterized by carat weight, color and so on. The carat weight is a universal standard for every gemstone but not the other criteria. For example the color range for diamond is not at all the same for a ruby, so I’d like to assign different custom fields to different categories of gemstones. And I would like the custom fields to vary according to the category of gemstone a seller decide to list on the listing page.
Could you tell me how should I do it please ?

Thank you !