The Journal of Gemmology Data Depository Photomicrographs to accompany the article: Hänni H.A., Brunk R. and Franz L. 2021. An investigation of grinding hardness of some ornamental stones. Journal of Gemmology, 37(6), 2021, 632–643, https://doi.org/10.15506/JoG.2021.37.6.632. The following photomicrographs of thin sections of the samples were made with a Leica DFC490 camera mounted on a Leica DMRD polarising microscope with transmitted light. For each sample, figure A shows the sample in plane-polarised light (II Pol.) and figure B with crossed polarisers (X Pol.); the sample numbers correspond to those in the article. Photomicrographs © L. Franz. 1 1 Aventurine quartz, green: Foliated matrix with aligned quartz (Qz) grains, fuchsite (Fu) tablets and accessory zircon (Zrn). 2 2 Aventurine quartz, orangey red: Mylonitic fabric with quartz (Qz) ribbons and recrystallized grains as well as intergrowths of muscovite with hematite (Ms & Hem). 3 3 Chalcedony, light grey: Intensely interlocked chalcedony (Chc) crystals with random orientation. 4 4 Chrysoprase: In a matrix of tiny chalcedony (Chc) and quartz (Qz) crystals, larger quartz aggregates occur. In microfractures, palisade-shaped chalcedony crystals and quartz grains formed. 5 5 Dumortierite: A banded texture with layers rich in dumortierite (Dum), dumortierite and quartz (Dum & Qz), quartz (Qz) and tourmaline (Tur). 6 6 Granite: The holocrystalline fabric is made up of subhedral plagioclase (Pl), orthoclase (Or), biotite (Bt) and anhedral quartz (Qz). 7 7 Green quartz: A granoblastic texture made up of large quartz (Qz) crystals as well as a microfolded layer of fuchsite (Fu). 8 8 Heliotrope (bloodstone): Green, brown and colourless accumulations of chalcedony (Chc) are recognizable. Roundish opaque phases are hematite (Hem). 9 9 Jadeite: An inhomogeneous texture with accumulations of jadeite (Jd), Cr-omphacite (Cr-Omp) and interspersed fluoro-richterite (F-Rct); aegirine (Ae) forms small, bluish green edges on fluoro-richterite. 10 10 Jasper, red: The banded texture consists of layers mainly made up of quartz (Qz), quartz-hematite (Hem) and of layers enriched in hematite with quartz and subordinate andradite (Adr). 11 11 Lapis lazuli: The sample shows an indistinct banding with layers rich in lazurite (Lzr) and layers bearing diopside (Di) and phlogopite (Phl). Accessories are calcite (Cal) and pyrite (Py). 12 12 Magnesite: Tiny crystals of magnesite (Mgs) form a matrix that is cut by numerous microfractures filled with quartz (Qz) and magnesite. 13 13 Malachite: The sample almost monomineralically consists of malachite (Mlc) fibres and shows alternating dark green and bright green layers. 14 14 Nephrite: Actinolite (Act) forms intensely intergrown, fibrous crystals with a random orientation and some larger prisms in fractures. 15 15 Obsidian, ‘mahogany’: The hyaline sample shows a flow structure with interwoven, colourless and pale brown obsidian (Obs) layers. Interspersed are crystals of sanidine (Sa). 16 16 Opal, pink (‘Andes opal’): The sample shows tufted palygorskite (Plg) enclosed in chalcedony, which is rimmed by hastate chalcedony (Chc) and small seams of opal (Opl). 17 17 Quartz, smoky: The quartz (Qz) crystal contains rutile (Rt) and tiny fluid inclusions. 18 18 Quartz, rose: The quartz (Qz) crystal shows fractures filled with limonite (Lm) or hematite (Hem). 19 19 Rhodochrosite: Large- and intermediate-sized rhodochrosite (Rds) crystals show rhombohedral crystal shapes. Adjacent are aggregates of tiny anhedral carbonate grains with pyrite (Py). 20 20 Rhodonite: Granoblastic rhodonite (Rdn) and porphyroblastic spessartine (Sps) appear in a randomly oriented manner. The rock is cut by numerous microfractures, which are largely filled with vernadite (V). 21 21 Sannan-Skarn: The sample shows an inhomogeneous, strongly deformed texture with a shear band cut by a fracture of the second generation filled with calcite (Cal). In the matrix and in other fractures, winchite (Wnc) and aegirine (Aeg) are found. 22 22 Sodalite: An isotropic mass of sodalite (Sdl) is cut by numerous microfractures in which the growth of calcite (Cal), natrolite (Ntr), paragonite (Pg) and alumohydrocalcite (Ahc) took place. 23 23 Sugilite: A fine-grained matrix consisting of sugilite (Sug) and quartz (Qz) crystals contains agglomerates of pectolite (Pct), phlogopite (Phl) and aegirine (Aeg). These minerals are also present in numerous microfractures. 24 24 Tiger’s-eye: The bimineralic sample consists of thin quartz (Qz) fibres collaterally intergrown with stems of goethite (Gth). 25 25 Verdite: Layers rich in fuchsite (Fu) and corundum (Crn) alternate with layers rich in margarite (Mrg). Retrograde diaspore (Dsp) and vermiculite (Vrm) form accumulations while rutile (Rt) is an accessory mineral. 26 .