Beryllium (esmi)
Beryllium is a exceedlingly diffeicult element to name in pure Icelandic. There's really only one word that is linked to the element and that's the loan-word "smaragður", "emerald", a greenish variety of beryl in which the element was discovered by Nichola-Louis Vauquelin in 1798. It exists in other languages as a feminine personal name: "Esmeralda" and the shorter form "Esme". I have no idea how well-known this portuguese name is in Icelandic. There is one person in Icelandic that has this name.
I decided to borrow this name for Portuguese in a way that it sounds genuine Icelandic: the neuter noun "esmi", which I choose because of it's sounding similar to "efni" and the i-shifted names of elements like "vetni" ("hydrogen", from "vatn" (water), "ildi" ("oxygen", from "eldur" (fire)), "lyfti" ("nitrogen", from "loft" (air), and my own construction : "kelki" ("calcium", from "kalk" (lime)), "telki" (magnesium, from "talk" (talk)", "selti" (chlorine, from "salt"), blyfti (radon, a fusion of "blý" (lead) + "-lyfti" (loft), "blýþungt loft").
So "esmi" is in my opinion the best option.
