Comparing visual and geochemical classification of limestone types : the Maltese globigerina limestone

Abstract

The untrained eye cannot distinguish between different types of Globigerina Limestone for fresh quarry samples. An effective, objective and repeatable methodology which permits such selection has now been established and published. This method, involving the use of Cluster Analysis on geochemical data, was originally developed for weathered quarry samples. Here badly weathered sol/ limestone and more durable franka limestone are very clearly identifiable. Initial work led to the identification of geochemical variables AlzO3, Si 02, K2O, Ti 02, Fe2Oi as discriminants between these two stone types. This paper illustrates the use of geochemical limits for these five oxides to classify freshly quarried samples from various quarries. Twenty-eight such samples were classified by quarry owners, on the basis of visual and tactile methods only, as being of the following types: bajda and safra (two franka types) and a soil type. If this geochemical method is deemed to be 100% fail-proof, the use of geochemical limits confirms the quarry owners' classifications as being 93% correct. Otherwise, it can be affirmed that there is 93% agreement between the visual and the numerical methodology. On the basis of these promising results, work is continuing to develop a simple and inexpensive classification system for Maltese Globigerina limestone.