How the character is built
The 石 radical marks this as a solid non-metal, and that is not a coincidence of this one character — it holds right across the table. Read the radical first and the element's state at room temperature is already settled.
One of the two homophones (with 锡 xī) that pushed the mainland to drop 矽 for silicon.
Where you actually meet it
富硒 (fùxī) selenium-enriched, seen on food packaging
The element itself
Selenium is one of a handful of elements that exists almost entirely as a by-product of something else: it substitutes for sulfur in copper ores, and is recovered from the sludge that collects beneath the anodes when copper is refined electrolytically. That sludge is one of the richest industrial materials there is, carrying selenium, tellurium, silver and gold together. Selenium's electrical resistance drops sharply when light falls on it, a property that ran the first light meters and, for decades afterwards, the drum inside every photocopier in every office.
Where it sits among the 118
First isolated in 1817.
In living things
Selenium is built into proteins as selenocysteine, the twenty-first amino acid, and it gets there by a trick that ought not to work: the cell reads a UGA stop codon as an instruction to insert it, prompted by a structure folded into the same messenger RNA. The point of all that machinery is that a selenol ionises more readily than the sulfur equivalent, making it a faster, more willing nucleophile — which is what the glutathione peroxidases and thioredoxin reductases exploit to strip peroxides out of the cell. Selenium's distribution in soil is famously patchy, and geochemists have mapped a broad low-selenium belt running across China from the northeast towards the southwest.
Where it comes from in China
Selenium's Chinese address is Enshi in western Hubei, where soils weathered from selenium-rich black shale carry unusually high levels of the element — enough that the district is known nationally for it and markets its produce on the strength of it. Selenium sits directly below sulfur in the periodic table and substitutes for it in pyrite, so it gathers wherever sulfide-rich, organic-rich muds piled up on an airless seafloor. It is also one of the few elements with a genuinely narrow window between too little and too much.
The full entry
For stroke order, example sentences, audio and the complete set of meanings, see the dictionary entry.
硒Selenium in the dictionary →Others built the same way
Every one of these carries 石, and every one is a solid non-metal.