Huntite-Hydromagnesite is a natural mineral mined in Greece and Turkey and sold by R.J. Marshall as C-TEC MC9. It is an approximately equal mixture of huntite, Mg3Ca(CO3)4, and hydromagnesite, Mg4(CO3)(OH)2∙3H2O, and is dried, crushed, finely ground, and classified to produce a white powder, the majority of its particles having less than 1 micron size. It gives off both water and carbon dioxide when heated, with a minor loss at about 230°C (thus, somewhat more thermally stable than ATH), and with major losses at about 420°C and 550°C; the total endotherm being about 1000 J/g and the total weight loss being about 53%. It provides approximately the same physical properties to a polyolefin as does ATH, and in some formulations, is found to have a cost vs. f. r. performance advantage. The huntite component contributes little to the endothermic effect at the decomposition temperature of most polymers but nonetheless has a positive benefit which is attributed to a heat barrier effect and reinforcement of the combustion residue.