Bergamo Ceppo's are special breccia stones found only at the foot of Mount Clemo and on the shore of Lake Iseo. The conglomeratic deposits emerge with extreme discontinuity along the western shore of the lake, from Costa Volpino down to just south of Castro, and at the mouth of the Val Borlezza, immediately upstream of that village.
These isolated plaques have been known since antiquity. Their petrographic and facies characteristics are very different from each other, their only common element being the lack of any direct relationship with other outcropping units. They are the result of an important phase in the Quaternary period, i.e. the mass demolition of rocky slopes and the accumulation of debris in powerful bodies, which as a whole are geologically referred to as the Poltragno complex. More specifically the latter includes the ceppo di Poltragno unit, the rocca di Castro unit, the San Maurizio unit and the Greno unit.
The material which this breccias consist of is predominantly Norian dolomite in angular fragments of varying sizes, strongly cemented by a light gray calcareous cement.
These stones are very popular in Italy and abroad: many buildings, both in historical times and in recent years, have seen the use of ceppo as the stone material for construction and finish. Bergamo ceppo’s are divided into three varieties, all extracted from quarries located between Castro and Pianico.
Ceppo di Gré. Now extracted in an underground quarry at Grè near Castro, it is defined as a strongly cemented brecciated dolomite, with good mechanical strength values that make it particularly suitable for coating applications. The rock lends itself to be processed in a variety of ways which allow its use in a wide range of realisations, thanks to its extreme versatility.
Ceppo di Poltragno and ceppo Brecciola. They represent two variants of the same lithological unit, extracted in several quarries at Poltragno (Pianico). It is a gray natural stone, very hard and porous, with a more ponderous presence of larger elements and rounded pebbles in the Brecciola. Thanks to its good technical properties, strong cementation and workability, these stone materials are suitable for an ample range of architectural uses.