There are a large number of allotropes of sulfur. In this respect, sulfur is second only to carbon. The most common form found in nature is yellow orthorhombic α-sulfur, which contains puckered rings of S8. Chemistry students may have seen "plastic sulfur"; this is not an allotrope but a mixture of long chain polymeric sulfur forms, two of which have been identified as allotropes. In addition to these there are other solid forms that contain sulfur rings of 6, 7, 9–15, 18 and 20 atoms. There are also gases, S2, S3; some species only detected in the vapour phase, S4 and S5 and perhaps five or more high-pressure forms, two of which are metallic.
The range of molecular allotropes possessed by sulfur can in part be ascribed to the wide range of bond lengths (180–260 pm) and bond angles (90–120°) exhibited by the S–S bond and its strength (the unrestrained S–S single bond has a high bond energy of 265 kJ mol−1).
Early workers identified some forms that have later proved to be allotropes, i.e. pure forms, whilst others have proved to be mixtures. Some forms have been named for their appearance, e.g. "mother of pearl sulfur", or alternatively named for a chemist who was pre-eminent in identifying them, e.g. "Muthmann's sulfur I" or "Engel's sulfur". A commonly used naming system uses Greek suffixes (α, β, etc.); however, this system predates the discovery of the new forms that have been synthesised rather than prepared from elemental sulfur.
Read more about Allotropes Of Sulfur: List of Allotropes and Forms, General Preparatory Strategies For cyclo-sulfur Allotropes, Solid Catena Sulfur Allotropes, Catena Sulfur Forms, High-pressure Forms