Geochemical and mineralogical analysis of stone anchors from west coast of India: provenance study using thin sections, XRF and SEM-EDS

Stone anchors have been recovered along the Indian coast as a part of the maritime archaeological studies at the National Institute of Oceanography (NIO), Goa. Study of stone anchors provides clues to understand the ancient maritime trade contacts of India with other countries. These anchors resemble those found in the Mediterranean Sea, Persian Gulf and Red Sea Coast. Underwater explorations at Bet Dwarka, Dwarka, Goa, Visawada and Somnath have yielded stone anchors of widely varying shapes, sizes and weights ranging between 16 and 410 kg. Sixteen (10 Indo-Arabian, 4 Ringstone and 2 Single hole type) of the total of 269 stone anchors have been studied to determine provenance of rock through petrographic analysis using thin section studies, X-ray Fluorescence (XRF), and Scanning Electron Microscope – Energy Dispersive Spectrometer (SEM-EDS).Our results suggest that these anchors were made from various rock types, such as granodiorite, dolerite, varieties of basalt, schist, calcareous sandstone, limestone and sandstone. The coastal tract of western India has exposures of all these rock types of igneous and sedimentary rock suites while ultramafic rocks occur inland along the Gujarat and Rajasthan border. It is inferred that these stone anchors have been sourced from rock formations from Gujarat, Goa, Karnataka and Maharashtra regions for use in maritime trading activities of the ancient and medieval periods.