The philosophers stone was an actual stone that was built up phosphorus derived from urine.

After urinating in the same pot or channel for many years the stone would build up and as an initiation into the orders they would make the initiates eat from the stone. Since a lot of people were lacking phosphorus in their diets those who ate the stones would live longer giving rise to the myth that the philosophers stone can give you eternal life.

Basically they discovered vitamins.

They turned lead into gold. Or dark ales the color of lead into urine which was gold. They say we all have the power within us to do this same thing.

They called themselves The Order of the Golden Dawn.

These people are stupid.