@misc{miscfbc8527d,
title   = {Opal-bearing sandstones as pozzolan material},
author = {Montanheiro, Tarcísio José and Coimbra, Armando Márcio and Gobbo, Luciano and Sayeg, Isaac Jamil and Atencio, Daniel},
year = {1999},
booktitle   = {Congress of the Brazilian Society for microscopy and microanalysis}
}