gem-

gem-

(jem),
Prefix denoting twin substitutions on a single atom, for example, the gem-dimethyl substitution on carbon-4 of lanosterol.
[L. geminus, twin]
References in periodicals archive ?
There are a number of scientific occurrences with no commercial potential elsewhere in the world, but this locality in the Coastal Ranges of California is the only economic concentration producing a significant quantity of gem- quality stones.