28. A vertically upright furnace for processing heat expandable ores such as perlite, vermiculite or the like, the furnace comprising: a rigid, upright frame adapted to be disposed upon a supporting surface; an elongated furnace tube adapted to be supported by said frame, the furnace tube including an upper product output orifice and a lower, reduced diameter heat input orifice; - means for preheating a raw ore and inputting pre heated ore into said furnace tube for expansion, the preheating means including: an elongated preheating enclosure secured to said furnace in heat exchange relation with' respect to said furnace tube; and, a plurality of heat conducting baffles for contacting and warming raw ore, the baffles adapted to be removably coupled within said enclosure in vertically spaced-apart, generally inclined relation therewithin; a generally tubular outer shell disposed coaxially about said furnace tube in spaced relation there with for forming an air cooling cavity there between; a preheating enclosure disposed interiorly of said air cooling cavity, an inner wall of said preheating enclosure being formed by said furnace tube, and said preheating enclosure includes spaced-apart, slotted side walls adapted to slidably, removably receive said baffles; and, means for injecting a stream of hot gas into said furnace tube to heat and thereby expand ore there within