left|thumb|Caesium crystals (golden) compared to rubidium crystals (silvery) Caesium forms alloys with the other alkali metals, gold, and mercury (amalgams). At temperatures below , it does not alloy with cobalt, iron, molybdenum, nickel, platinum, tantalum, or tungsten. It forms well-defined intermetallic compounds with antimony, gallium, indium, and thorium, which are photosensitive. It mixes with all the other alkali metals (except lithium); the alloy with a molar distribution of 41% caesium, 47% potassium, and 12% sodium has the lowest melting point of any known metal alloy, at . A few amalgams have been studied: is black with a purple metallic lustre, while CsHg is golden-coloured, also with a metallic lustre.
left|thumb|Caesium crystals (golden) compared to rubidium crystals (silvery) Caesium forms alloys with the other alkali metals, gold, and mercury (amalgams). At temperatures below , it does not alloy with cobalt, iron, molybdenum, nickel, platinum, tantalum or tungsten. It forms well-defined intermetallic compounds with antimony, gallium, indium, and thorium, which are photosensitive. It mixes with all the other alkali metals (except lithium); the alloy with a molar distribution of 41% caesium, 47% potassium, and 12% sodium has the lowest melting point of any known metal alloy, at . A few amalgams have been, studied: is black with a purple metallic lustre, while CsHg is golden-coloured, also with a metallic lustre.