"Gneiss!": a relatively soft stone used for decorative work. As such, it is used as a minor complement, or if said with vigor, a backhanded complement/minor insult. To say someone is gneiss is to say they look good or put up an attractive façade, but are of little substance.
"Schist!": used same way as gneiss, above, for the same reasons.
Since these words are "false friends"* to words in Common, their use sometimes leads to misunderstandings...
* "False Friends" are words that sound like words in another language or dialect, but have completely different meanings. Example: "rubber" in standard British use means "eraser", but in standard American slang means "condom."
"Schist!": used same way as gneiss, above, for the same reasons.
Since these words are "false friends"* to words in Common, their use sometimes leads to misunderstandings...
* "False Friends" are words that sound like words in another language or dialect, but have completely different meanings. Example: "rubber" in standard British use means "eraser", but in standard American slang means "condom."