Zeolite characterization of 'Vico red tuff with black scoria' ignimbrite flow: The extractive district of Civita Castellana (Viterbo, Italy)

The results of the work undertaken on one of the major ignimbrite flows of northern Lazio in Italy, the so-called “Vico red tuff with black scoria” are reported. A survey of bed thickness, carried out on the working faces of different quarries revealed that the available data in the literature underestimated the size of the deposit. The extension of the studied area, named as the “extractive district of Civita Castellana”, has been estimated to be about 150 km2 with a volume of not less than 5.5km3. XRD analysis indicated a high zeolite content in the tuffs ranging from 29% to 67%. The most abundant species are chabazite which predominates andoccurs mainly in the matrix of the rock, and phillipsite in smaller proportion chiefly found in the scoria fraction. The cation exchange capacity (CEC) was determined either directly by ion exchange or estimated combining EDS elemental analyses with XRD data, and the differences between the two applied methods are discussed. The CEC values are in the range 1.65 to 2.20 meq/g with Ca++ and K+ as the main components. By removing completely Ca++ a limit value of 2.40 has been reached. Parent materials have been tested for removal of NH4+ from dilute solutions. The chemical and mineralogical characteristics of this material combined with its high availability at outcrop enables new horizons to be opened up with good prospects for diverse fields of application and a promising economic potential.