View source for Electrically conductive gem-like compounds

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A subgroup of [[diamondoid compounds]]. <br>
Conductive compounds in thicker layers do not let light pass but do reflect it instead.
See wikipedia: [http://en.wikipedia.org/wiki/Plasma_oscillation plasma frequency]

* hematite, magnetite, pyrite, ... 
* members of the spinell mineral group with metallic conductivity
* some copper and lead sulfide compounds
* in an AP pattern doped silicon and diamond (rather low level metamaterials than compounds)

Often high level [[diamondoid metamaterial]] might be a batter choice like crosshatched conductive nanotubes.
One direction only would let through polarized light.