Sulfur or sulphur

Sulfur or sulphur; the spelling difference is mainly a question of AmE vs other English speaking countries as suggested by the Grammarist. For the pale yellow nonmetallic element found especially in volcanic deposits, sulfur is the usual spelling in American English.

Sulphur is generally the preferred spelling in nonscientific texts from outside North America, but sulfur is gaining ground in scientific writing throughout the English-speaking world

The spelling distinction extends to derivative words such as sulfuric/sulphuric, sulfate/sulphate, and sulfide/sulphide. Usually English words spelled with 'ph' are derived from Greek, where the 'ph' represents the Greek letter ‘phi’, but in this case the ultimate source of the word is Arabic.

The word, from the French soufre, entered English around the end of the 14th century. Both modern spellings have been in use for many centuries, but sulphur prevailed by a wide margin until the Americans adopted sulfur around the start of the 20th century as shown in Ngram.

 Sulfur (in traditional lay Commonwealth English: sulphur) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula S8. Elemental sulfur is a bright yellow, crystalline solid at room temperature.

Sulfur is the tenth most common element by mass in the universe, and the fifth most common on Earth. Though sometimes found in pure, native form, sulfur on Earth usually occurs as sulfide and sulfate minerals.