section_path: Characteristics/Allotropes
section_name: Allotropes
paragraph_text: Allotropes
  
  Sulfur forms over 30 solid allotropes, more than any other element. Besides S, several other rings are known. Removing one atom from the crown gives S, which is of a deeper yellow than S. HPLC analysis of "elemental sulfur" reveals an equilibrium mixture of mainly S, but with S and small amounts of S. Larger rings have been prepared, including S and S.
  
  Amorphous or "plastic" sulfur is produced by rapid cooling of molten sulfur—for example, by pouring it into cold water. X-ray crystallography studies show that the amorphous form may have a helical structure with eight atoms per turn. The long coiled polymeric molecules make the brownish substance elastic, and in bulk this form has the feel of crude rubber. This form is metastable at room temperature and gradually reverts to the crystalline molecular allotrope, which is no longer elastic. This process happens within a matter of hours to days, but can be rapidly catalyzed.