ABSTRACT

Fused tuff and tuffaceous rocks have been found at seven localities in the Manning Formation of the Jackson Group in the Texas Gulf Coastal Plain. The distribution of these localities extends along the strike of the Manning Formation from Trinity County to Fayette County.

There are four kinds of fused material: (1) reddish, hardened, brick-like partially fused tuff and tuffaceous siltstone that has fused in place; (2) brittle, glassy or porcelaneous, gray, red-brown or black fused tuffaceous material that has melted in place; (3) vesicular, glassy fused tuff that has been injected and intruded into channel sandstone; and (4) clinker-like, vesicular, partly crystalline, pseudo-basalt that has flowed into fractures and cavities in the partially fused tuffaceous rocks.

The rocks were fused at each locality by heat generated from the burning of an underlying thin lignite bed. Volume reduction following the burning of the lignite led to collapse of overlying beds, and extensive fracturing and deformation of these partially fused rocks.

Artificial dry fusion at 1250° C. and one atmosphere pressure of tuff from one locality produced glassy material similar to natural fused tuff.