Photograph of polarised thin section of stone axe (ISAP 00073) from Ballycastle, Co. Antrim, from the National Museum of Ireland (NMI SA 1927:14). Macro-ID - Porcellanite. Micro-ID - Porcellanite Ia. Petrology - Grey, banded coarse mottled. Description - Sides - Facetted, right broader than left. Junction of sides with edge present on right, damaged on left. No clear junctions of sides with butt. Edge - Ground flat (resharpening?), Sinuous in profile. Blade Area - Face 1 left side lower portion has a single medium sized post-manufacture flake scar, and the grinding of the edge encroaches onto this damaged surface, (i.e. this damage is the reason for the resharpening?). Small patch of lichen/encrustation Face 1 right side. Faces - Two to three small remnant flake scars adjacent to both sides, both faces. Face 2 slightly flattened along centre, upper portion. Overall moderate degree of polish. Butt - Original, only partially ground, irregular surface, slopes from Face 1 to Face 2. Core taken from Face 1. Dimensions (length x width x thickness) - 11.2 cm, 4.1 cm, 2.8 cm, 212g.