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Four allotropes of antimony are known, a stable metallic form and three metastable forms, explosive, black and yellow.
Metallic antimony is a brittle, silver-white shiny metal.
When molten antimony is slowly cooled, metallic antimony crystallizes in a trigonal cell, isomorphic with that of the gray allotrope of arsenic.
A rare explosive form of antimony can be formed from the electrolysis of antimony ( III ) trichloride.
When scratched with a sharp implement, an exothermic reaction occurs and white fumes are given off as metallic antimony is formed ; when rubbed with a pestle in a mortar, a strong detonation occurs.
Black antimony is formed upon rapid cooling of vapor derived from metallic antimony.
It has the same crystal structure as red phosphorus and black arsenic, it oxidizes in air and may ignite spontaneously.
At 100 ° C, it gradually transforms into the stable form.
The yellow allotrope of antimony is the most unstable.
It has only been generated by oxidation of stibine ( SbH < sub > 3 </ sub >) at − 90 ° C.
Above this temperature and in ambient light, this metastable allotrope transforms into the more stable black allotrope.

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