|Other names||mercuric iodide|
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|Molar mass||454.40 g/mol|
|Appearance||scarlet red powder|
|Density||6.36 g/cm³, solid|
|Except where noted otherwise, data are given for|
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references
Mercury(II) iodide displays thermochromism; when heated above 126 °C, it undergoes phase transition from the alpha crystalline form to a pale yellow beta form. As the sample cools, it gradually reacquires its original color. It is often used for thermochromism demonstrations. 
In medicine, mercury(II) iodide was formerly used as a treatment for syphilis.
Mercury(II) iodide is one of the stated possibilities for the "red mercury".