Editing Californium (section)

=== Physical properties ===
Californium is a silvery-white [[actinide]] metal{{sfn|Jakubke|1994|p=166}} with a [[melting point]] of {{convert|900|±|30|C|-1}} and an estimated [[boiling point]] of {{convert|1743|K|-1}}.{{sfn|Haire|2006|pp=1522–1523}} The pure metal is malleable and is easily cut with a knife. Californium metal starts to vaporize above {{convert|300|C|-1}} when exposed to a vacuum.{{sfn|Haire|2006|p=1526}} Below {{convert|51|K|C F|0|abbr=on}}<!-- KEEP KELVIN --> californium metal is either [[ferromagnetism|ferromagnetic]] or [[ferrimagnetism|ferrimagnetic]] (it acts like a magnet), between 48 and 66&nbsp;K it is [[antiferromagnetism|antiferromagnetic]] (an intermediate state), and above {{convert|160|K|C F}}<!-- KEEP IN KELVIN (−110&nbsp;°C) --> it is [[paramagnetic]] (external magnetic fields can make it magnetic).{{sfn|Haire|2006|p=1525}} It forms [[alloy]]s with [[lanthanide]] metals but little is known about the resulting materials.{{sfn|Haire|2006|p=1526}}

The element has two [[Crystal structure|crystalline forms]] at [[Standard atmosphere (unit)|standard atmospheric pressure]]: a double-[[Close-packing of equal spheres|hexagonal close-packed]] form dubbed alpha (α) and a [[Cubic crystal system|face-centered cubic]] form designated beta (β).{{efn|A double hexagonal close-packed (dhcp) [[unit cell]] consists of two hexagonal close-packed structures that share a common hexagonal plane, giving dhcp an ABACABAC sequence.{{sfn|Szwacki|2010|p=80}} }} The α form exists below 600–800&nbsp;°C with a density of 15.10&nbsp;g/cm<sup>3</sup> and the β form exists above 600–800&nbsp;°C with a density of 8.74&nbsp;g/cm{{sup|3}}.{{sfn|O'Neil|2006|p=276}} At 48&nbsp;[[pascal (unit)|GPa]] of pressure the β form changes into an [[orthorhombic crystal system]] due to delocalization of the atom's [[Electron shell|5f electrons]], which frees them to bond.{{sfn|Haire|2006|p=1522}}{{efn|The three lower-mass transplutonium elements—[[americium]], [[curium]], and [[berkelium]]—require much less pressure to delocalize their 5f electrons.{{sfn|Haire|2006|p=1522}} }}

The [[bulk modulus]] of a material is a measure of its resistance to uniform pressure. Californium's bulk modulus is {{val|50|5|u=GPa}}, which is similar to trivalent lanthanide metals but smaller than more familiar metals, such as aluminium (70&nbsp;GPa).{{sfn|Haire|2006|p=1522}}