This problem has puzzled me for a long time i always think about why stranded people on islands cant make a proper civilization and i always think it comes down to the ability to work metal. But its not like they could make a steel smelter/furnace out of sand...they would need an older one to use to make the new one...where the hell did the first one come from then????
it is a problem to work metals thats why the first furnaces were for metals with a low melting point eg copper. To built a furnace for iron you need a very high temperature and for steel additional chemical treatment probably not available on an island. To smelt iron should be possible though as a clay furnace with the right coal is hot enough to produce raw iron.
You don't need steel to make a smelter. Early ones were made of simple materials such as stone (though the first ones developed would be to smelt gold, then bronze, then iron-widespread use of steel is a relatively late innovation) A desert island resident however would be unlikely to have the skills, nor the iron ore to make one.
originally steel was made by hand- by hammering an iron ingot (easily obtained from turf iron), heating it in coal (allows the carbon to penetrate the iron) then folding it and hammering it again- several hundred times. with each such procedure the iron absorbs more carbon and becomes steel of course steel smelters made this process simpler- but then you can't get damascene steel out of a smelter... the island civilisations could make smelters out of clay. But finding clay or iron ore on a coral island would be a forlorn task
