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.

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1 , : Foliated matrix with aligned quartz (Qz) grains, fuchsite (Fu) tablets and accessory zircon (Zrn).

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2 Aventurine quartz, orangey red: Mylonitic fabric with quartz (Qz) ribbons and recrystallized grains as well as intergrowths of with (Ms & Hem).

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3 Chalcedony, light grey: Intensely interlocked chalcedony (Chc) with random orientation.

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4 : 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.

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5 Dumortierite: A banded texture with layers rich in dumortierite (Dum), dumortierite and quartz (Dum & Qz), quartz (Qz) and (Tur).

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6 : The holocrystalline fabric is made up of subhedral plagioclase (Pl), orthoclase (Or), biotite (Bt) and anhedral quartz (Qz).

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7 Green quartz: A granoblastic texture made up of large quartz (Qz) crystals as well as a microfolded layer of fuchsite (Fu).

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8 Heliotrope (bloodstone): Green, and colourless accumulations of chalcedony (Chc) are recognizable. Roundish opaque phases are hematite (Hem).

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9 : 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.

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10 , 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).

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11 : The sample shows an indistinct banding with layers rich in lazurite (Lzr) and layers bearing (Di) and phlogopite (Phl). Accessories are (Cal) and (Py).

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12 Magnesite: Tiny crystals of magnesite (Mgs) form a matrix that is cut by numerous microfractures filled with quartz (Qz) and magnesite.

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13 : The sample almost monomineralically consists of malachite (Mlc) fibres and shows alternating dark green and bright green layers.

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14 : Actinolite (Act) forms intensely intergrown, fibrous crystals with a random orientation and some larger prisms in fractures.

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15 , ‘mahogany’: The hyaline sample shows a flow structure with interwoven, colourless and pale brown obsidian (Obs) layers. Interspersed are crystals of sanidine (Sa).

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16 , (‘Andes opal’): The sample shows tufted palygorskite (Plg) enclosed in chalcedony, which is rimmed by hastate chalcedony (Chc) and small seams of opal (Opl).

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17 Quartz, smoky: The quartz (Qz) contains rutile (Rt) and tiny fluid inclusions.

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18 Quartz, rose: The quartz (Qz) crystal shows fractures filled with limonite (Lm) or hematite (Hem).

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19 Rhodochrosite: Large- and intermediate-sized rhodochrosite (Rds) crystals show rhombohedral crystal shapes. Adjacent are aggregates of tiny anhedral carbonate grains with pyrite (Py).

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20 : Granoblastic rhodonite (Rdn) and porphyroblastic (Sps) appear in a randomly oriented manner. The rock is cut by numerous microfractures, which are largely filled with vernadite (V).

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21 Sannan-Skarn: The sample shows an inhomogeneous, strongly deformed texture with a shear band cut by a of the second generation filled with calcite (Cal). In the matrix and in other fractures, winchite (Wnc) and aegirine (Aeg) are found.

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22 : 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.

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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.

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24 Tiger’s-eye: The bimineralic sample consists of thin quartz (Qz) fibres collaterally intergrown with stems of goethite (Gth).

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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.

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