“The Masked World,” Jack Williamson, 1963 — An astronaut searches for his wife, Lilith. Lilith was part of a survey tasked with “reading” the genetic code of the life there with advanced genetic probes. Upon reconstructing Lilith’s work, the protagonist discovers that she’s left him a message using copper and arsenic atoms inserted into a genetic code: The life on the planet is pseudomorphic.
Comments: Read in At the Human Limit.
Author: Wikipedia: “John Stewart Williamson (April 29, 1908 – November 10, 2006), who wrote as Jack Williamson (and occasionally under the pseudonyms Will Stewart and Nils O. Sonderlund) was a U.S. writer often referred to as the ‘Dean of Science Fiction’ following the death in 1988 of Robert A. Heinlein.”