Sulfur occurs uncombined in volcanic and sedimentary deposits, as well as being a constituent of many minerals and petroleum. It is normally a bright yellow crystalline solid, but several other allotropic forms can be made. Sulfur is an ingredient of gunpowder, and is used in making matches and as an antiseptic and fungicide
Middle English: from Anglo-Norman French sulfre, from Latin sulfur, sulphur
The standard US spelling is sulfur; sulphur is the traditional British spelling. However, the -f- spelling is now standard in scientific and technical writing in the UK, and is increasingly used in other contexts as well.
Spell sulfur and the words related to it such as sulfate and sulfuric with an f in the middle. Spellings with a -ph- are British: sulphur, sulphate, sulphuric.