We consider a small sample of oxygen-rich , asymptotic giant branch stars in the Large Magellanic Cloud , observed by the Spitzer Space Telescope , exhibiting a peculiar spectral energy distribution , which can be hardly explained by the common assumption that dust around AGB stars is primarily composed of silicate grains .
We suggest that this uncommon class of objects are the progeny of a metal-poor generation of stars , with metallicity Z \sim 1 - 2 \times 10 ^ { -3 } , formed \sim 100 Myr ago .
The main dust component in the circumstellar envelope is solid iron .
In these stars the poor formation of silicates is set by the strong nucleosynthesis experienced at the base of the envelope , which provokes a scarcity of magnesium atoms and water molecules , required to the silicate formation .
The importance of the present results to interpret the data from the incoming James Webb Space Telescope is also discussed .