Editing Calcium (section)

===Physical properties===
Calcium metal melts at 842&nbsp;°C and boils at 1494&nbsp;°C; these values are higher than those for magnesium and strontium, the neighbouring group 2 metals. It crystallises in the [[face-centered cubic]] arrangement like strontium and barium; above {{convert|443|C|K}}, it changes to a [[body-centered cubic]].<ref name="Arblaster 2018" /><ref name="Smith 1956">{{cite journal |last1=Smith |first1=J. F. |last2=Carlson |first2=O. N. |last3=Vest |first3=R. W. |title=Allotropic Modifications of Calcium |journal=Journal of the Electrochemical Society |volume=103 |date=1956 |issue=7 |doi=10.1149/1.2430364 |page=409}}</ref> Its density of 1.526&nbsp;g/cm<sup>3</sup> (at 20&nbsp;°C)<ref name="Arblaster 2018" /><!-- ref name="Arblaster 2018" is defined in infobox: {{cite book |last=Arblaster |first= John W. |title=Selected Values of the Crystallographic Properties of Elements |publisher=ASM International |publication-place=Materials Park, Ohio |date=2018 |isbn=978-1-62708-155-9}}--> is the lowest in its group.{{sfn|Greenwood|Earnshaw|1997|pp = 112-13}}

Calcium is harder than [[lead]] but can be cut with a knife with effort. While calcium is a poorer conductor of electricity than [[copper]] or [[aluminium]] by volume, it is a better conductor by mass than both due to its very low density.{{Sfn|Hluchan|Pomerantz|2005|p=484}} While calcium is infeasible as a conductor for most terrestrial applications as it reacts quickly with atmospheric oxygen, its use as such in space has been considered.{{Sfn|Hluchan|Pomerantz|2005|p=484}}