Thank you all for your responses

@Richard - At the moment no, they only probably need a human readable name for the moment. If I need to add more information later like a sales prices or such I was thinking of creating a generic SalesItem where the specific is composited into that new item. - Or what ever the common practice equivalent for this would be in F#.

@Brian - thank you - I will try and give that approach a go today if I get time. It looks promising, visually. I'll be interested to see how my "operations" functions work with it. It looks close to what I want to achieve in my mind.

@Brent - The plan is to only allow new materials and behaviours for them through new hardcoded types. I understand with F# pattern matching I could probably have a single type with a differentiator say "Ore", "Oil" "Gas" and then have a Name "Iron Ore", "Coal Ore", "Crude Oil", "Natural Gas" but then I would assume I will have some massively long "match" expressions that will have to grow with each new type, anyway? Or am I looking at this wrong.

Sorry for answering to all in a single reply, but normally in Stack Overflow I would comment on each reply, but for some reason SO is not giving me that option today!