tuff breccia - display specimen of a spectacular tuff breccia with a variety of clast types embedded in the pinkish ash
This particular volcanic igneous rock is composed of volcanic ash and many fragments (clasts) of other igneous rocks that were ejected from a volcanic vent. Because the ash was very hot when it fell to earth, the ash and rock fragments were welded together.
A breccia (from the Italian breccia for rubble) is normally composed of angular broken rock fragments that have been cemented together, such as where faulting has shattered rocks. In this case, there are so many broken fragments in this tuff that it is called a tuff breccia. The angular fragments in a breccia show that the fragments were cemented where they were formed. If they had been transported by running water, the edges would have become rounded.
Tuffs are light colored, usually shades of buff or gray, and since they are silica rich, they are not dense. This pink tuff is spectacular, in part because of the varied clasts. A student should know that angular clasts, from the Greek klastos for broken in pieces, are characteristic of tuffs.
This specimen is larger than usual and shows a dramatic variety of clasts, the fragments of other rocks that were ripped from the vent and embedded in the welded pink ash. This is an amazing tuff!
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