Optical microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) datasets obtained using stromatolites samples from Lake Ashenge, Tigray, Ethiopia

Optical microscopy and SEM-EDS data acquired from a sample of stromatolites growing over basalt at Lake Ashenge, Ethiopia. Data are presented in the following forms: – Optical microscopy data are provided as .png files. – SEM images are provided as .png files. – SEM-EDS datasets are provided as .oip files that may be be opened directly in Oxford Instruments AZtec software. Optical microscopy was performed using an Olympus BX63 system equipped with ×2, ×5, ×10, ×20 and ×40 objectives and a CCD camera (Imaging and Analysis Centre, NHM London, UK). Images were acquired using Olympus CellSens software. SEM imaging of rock fragments was performed using a JEOL JXA-8100 electron probe microanalyser at Birkbeck, University of London operating at a working distance of 10 mm, a current of 20 nA, and an accelerating voltage of 15 kV. Rock fragments were carbon coated (~10 nm coating) prior to analysis. SEM-EDS analyses of large regions (up to several square millimetres) of selected thin sections were performed using a JEOL IT500 system equipped with an Oxford Instruments X-Max EDS detector, operating at a working distance of 11 mm and an accelerating voltage of 15 kV (Imaging and Analysis Centre, NHM London). Thin sections were uncoated and observed under environmental conditions.