• Boulangerite crystals from Pribram, Czechia. Their diameter is in the order of 0.1 mm, similar to human hair.
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    Stacks Image 1236
  • microscopic Agardite rods from the German Clara mine (12.5x magnification).
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    Stacks Image 1266
  • Obsidian from the Ethiopian volcano Erta Ale (f.o.v. ≈ 5 mm).
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    Stacks Image 1234
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    Birefringence is caused by shear bands in the vitreous material.
    Sir C.V. Raman reported similar observations with plate glass in:
    Proc. Ind. Acad. Sci. A, 31 (1950) 359
  • Moldavite from Bohemia (f.o.v. ≈ 18 mm).
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    Stacks Image 1316
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    Translucent, mossy green tektites of vitreous silica originate from the Ries Crater (15 millions years ago, Bavaria) and are found in Bohemia.
  • Prehistoric artifact from Mauritania (f.o.v. ≈ 3 cm).
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    Stacks Image 1320
  • Eroded stibnite (Sb2S3) with the yellow degradation product valentinite (Sb2O3) from Poiana Botizii, Romania (f.o.v. ≈ 2 cm).
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    Stacks Image 1254
  • Aragonite (CaCO3) from Hildfeld, Germany (f.o.v. ≈ 17 mm).
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    Stacks Image 1354
  • Iridescent layer in a Mexican fire agate (f.o.v. ≈ 5 mm).
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    Stacks Image 183
  • Glimmer of a micaceous mineral of unknown origin (f.o.v. ≈ 4 mm).
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    Stacks Image 1352
  • Abalone shell from the Senegalese coast (f.o.v. ≈ 1 cm).
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    Stacks Image 1292
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    Haze and black speckles are caused by the outer translucent layer which is partly eroded near the fringe.
  • Strontianite (SrCO3) from Beckum, Germany (f.o.v. ≈ 2 cm).
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    Stacks Image 1278
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    The mineral was named after the Scottish locality Strontian. In the second half of the 19th century it was used for the sugar extraction from molasses by making use of the reversible transformation of the carbonate into the hydroxide (via the intermediate oxide) which reacts with the sugar. Strontium was recovered as SrCO3 from the precipitated Sr-(glucose)2 through the reaction with carbon dioxide. The process, invented by Carl Scheibler in 1863, lost profitability already in the eighties when cheaper SrSO4 and cane sugar were imported from England and European colonies, respectively.
  • Etched slice from the iron nickel meteorite Gibeon, Namibia (impact 13-30 thousand years ago, f.o.v. ≈ 22 mm).
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    Stacks Image 1296
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    Metallic Fe-Ni phases (Widmanstätten pattern, cf. dedicated slide) are surrounding black troilite (FeS). This iron sulfide mineral is barely found outside of meteorites on Earth, whereas it represents one percent of the lunar surface.
  • Petrified shell from the Egyptian White Desert (f.o.v. ≈ 15 mm).
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    Stacks Image 1286
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    Note the partially blasted black desert varnish.
  • Amethyste crystallites (up to 4 mm large) at the bottom of a geode, backlit with white LED light.
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    Stacks Image 1288
  • Unusually compact desert rose from the Mauritanian Sahara (f.o.v. ≈ 2 cm).
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    Stacks Image 1368
  • Realgar (As4S4) crystals from Morocco (f.o.v. ≈ 2 cm).
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    Stacks Image 1382
  • Dumortierite rods of unknown origin (f.o.v. ≈ 8 mm).
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    Stacks Image 1394
  • Vanadinite (Pb5(VO4)3Cl) from Morocco, (f.o.v. ≈ 1 cm).
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    Stacks Image 1389
  • Charoite from Yakutia, Russia (f.o.v. ≈ 2 cm).
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    Stacks Image 1406
  • Madagascan iridescent ammonite (f.o.v. ≈ 25 mm).
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    Stacks Image 1384
  • Pentagonite from Wagholi, Pune, India (f.o.v. ≈ 15 mm).
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    Stacks Image 1302
  • Etched slice of the Mounionalusta iron nickel meteorite. Impact was a million of years ago in nowadays Sweden (f.o.v. ≈ 27 mm).
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    Stacks Image 1346
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    Widmanstätten pattern consisting of dark bars of taenite (< 10 % Ni, 1-2 mm wide) and bright parallel lines within kamacite (20-65 % Ni). The latter Neumann lamellae reflect crystal deformation.
  • Galena (PbS) from the Katerina coal mine in Radvanice, Czechia (f.o.v. ≈ 4 mm).
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    Stacks Image 1260
  • Pink erythrite crystals besides quartz on Bi-Co-Ni ore from the Bergkappe mine shaft in Schneeberg, Germany (f.o.v. ≈ 17 mm).
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    Stacks Image 1410
  • Scarlet cinnabar (HgS) with yellow siderite (FeCO3) and quartz from the Erzberg, Austria (f.o.v. ≈ 12 mm).
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    Stacks Image 1256
  • Layered sediments of lime stone in the Egyptian White Desert intercalate dust and sand grains (f.o.v. ≈ 1 cm).
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    Stacks Image 1414