Brimstone is the lemon coloured stone found at the brim of volcanoes and hot springs. This chemical is now more usually known by its Latin name 'sulfur'1, and the term 'brimstone' tends to be reserved for references in ancient texts such as the Bible2.
Alchemists have used different symbols for sulfur, including the upward-pointing triangle surmounting a cross. The triangle in alchemy symbolises fire, and the cross symbolises earth.
There is an interesting similarity with Chinese and Japanese characters where 'fire' is shown as and 'earth' is represented as . Similarly with the double-barred cross of the brimstone symbol, the character for 'out' is , which may be an old pictogram for an erupting volcano3.
Sulphur happens to be an element that is essential for life and it is no coincidence that the same symbols are used in Christianity4. The triangle and the cross symbolise the divinity of Christ and salvation. The cross represents life and when this is combined with the infinity symbol the meaning is everlasting life.