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Which halogen forms dark violet crystals at room temperature?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — halogen Modern version of the periodic table of the elements.

The halogen that forms dark violet crystals at room temperature is iodine.

While iodine appears as a nearly black, glittering crystalline solid at room temperature, it has a moderate vapor pressure and slowly sublimes into a characteristic deep violet vapor. This distinct violet color is also observed when iodine is dissolved in inert solvents such as carbon tetrachloride or carbon disulfide.123