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.
Stone radical, not metal — the namers classed astatine with the solid non-metals. (Astatine is usually called a non-metal or a metalloid, and even its solid state is a prediction: no visible piece has ever existed.) Taiwan writes a different character, 砈, read è.
This character is used for the element and little else — you are unlikely to meet it outside a chemistry classroom.
The element itself
Astatine is the rarest naturally occurring element on Earth. It exists only as a fleeting step in the decay chains of uranium and thorium, and every atom that forms is gone within hours, so the standing quantity in the entire crust at any instant is estimated at well under a gram. Nobody has ever seen a visible sample and probably nobody ever will: enough astatine to look at would generate so much heat from its own radioactivity that it would vaporise itself.
Where it sits among the 118
First isolated in 1940.
The full entry
For stroke order, example sentences, audio and the complete set of meanings, see the dictionary entry.
砹Astatine in the dictionary →Others built the same way
Every one of these carries 石, and every one is a solid non-metal.