How the character is built
The 钅 radical marks this as a 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. It is 金 (jīn) squeezed into the space beside another component — radicals change shape by position, which is why 金 is hard to spot until you know to look for 钅.
Mainland 锎 kāi (phonetic 开); Taiwan writes 鉲 kǎ, which sits closer to 'Cali-'.
This character is used for the element and little else — you are unlikely to meet it outside a chemistry classroom.
The element itself
Californium-252 is one of the very few substances that emits neutrons purely by sitting there, through spontaneous fission, and a microgram of it is a portable neutron source that needs no accelerator. That makes it genuinely useful — starting up reactors, scanning for explosives, logging boreholes to identify what rock the drill is in — and also one of the most expensive materials on Earth by weight, produced a few milligrams a year in a handful of reactors capable of the long neutron bombardment it takes to build a nucleus that heavy.
Where it sits among the 118
First isolated in 1950.
The full entry
For stroke order, example sentences, audio and the complete set of meanings, see the dictionary entry.
锎Californium in the dictionary →Others built the same way
Every one of these carries 钅, and every one is a metal.