Editor: M. Franklin
IGA Newsletter 2020
February 2021
Report on IGA Field Trip to Dundrum Town Centre Shopping Mall
Date: 14th August, 2019
This field trip needed neither rain gear nor hiking boots! Expertly led by Susan Pyne, its purpose was to examine the beautiful dimension stones that pave the shopping mall on different levels, inside the Dundrum Town Centre development. This shopping mall was opened in 2005 and the polished paving slabs have been sourced from such faraway places as South Africa and the Himalayas. They provide examples of the three main types of rock: igneous, metamorphic and sedimentary. Dimension stones in Dundrum Town Centre The first location visited was on Level 3, where the floor of the mall is paved with a type of GNEISS. Susan explained that this is a metamorphic rock, formed when the original igneous rock was subjected to heat and great pressure. The polished stone shows bands of pink material, alternating with darker bands, which are almost black. The crystals are aligned in particular directions, caused by the pressure to which they were subjected. Tiny garnet crystals are present.This stone probably came from South Africa. (See Photo on the right:)
Gneiss from South Next, we descended to Level 1, to examine a green polished stone, which, Susan told us, originated deep within the Earth’s mantle as PERIDOTITE. The main mineral present is OLIVINE, which is a silicate of magnesium and/or iron. It contains individual SiO44- ions, whose charge may be balanced by two Fe2+ ions, or two Mg2+ ions, or both. In fact, olivine forms a solid solution whose composition ranges from Fe2SiO4 to FeMgSiO4 to Mg2SiO4 and everything in between. Being rich in magnesium (Mg) and iron (Fe), it is classified by geologists as a mafic material. In this particular stone, the original olivine has been weathered by contact with water, to form SERPENTINE. In addition, the rock has become broken up into sharp pieces and then cemented together to form a type of BRECCIA. Builders refer to this polished stone as serpentine ‘marble’, but in fact it is not really marble as a geologist would understand the term.
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Serpentine Breccia
