If "Gas" belongs to "State of Matter" then what does "Metal" belong to?
"Metal" is a classification used by chemists and usually means something along the lines of "this electrically conductive, usually solid element that is deformable". 

The other way around: Chemists use "gas" to refer to a state of matter, not some defined gas (for example the atmosphere).

Putting these two together: "Metal" belongs to the periodic table of elements, while "solid", "liquid", "gas" and "plasma" are merely words to describe what state the element or compound is in. It is possible to have liquid, solid or even gaseous metals.

Edit: If you want a name for a variable that is either in the state Metal, Half-Metal or Metalloid and Non-Metal, I'm not sure such a name even exists. Feel free to make one up that suits your needs, comment your code sufficiently and it will not be a problem. "Metallicness" or something along those lines would be my choice.