illustris | photography

microscopic Agardite rods from the German Clara mine (12.5x magnification).
____

Obsidian from the Ethiopian volcano Erta Ale (f.o.v. ≈ 5 mm).
____

___
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).
__

__
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).
__

Eroded stibnite (Sb₂S₃) with the yellow degradation product valentinite (Sb₂O₃) from Poiana Botizii, Romania (f.o.v. ≈ 2 cm).
__

Aragonite (CaCO₃) from Hildfeld, Germany (f.o.v. ≈ 17 mm).
__

Iridescent layer in a Mexican fire agate (f.o.v. ≈ 5 mm).
__

Glimmer of a micaceous mineral of unknown origin (f.o.v. ≈ 4 mm).
__

Abalone shell from the Senegalese coast (f.o.v. ≈ 1 cm).
__

__
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).
__

__
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).
__

__
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).
__

__
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.
__

Unusually compact desert rose from the Mauritanian Sahara (f.o.v. ≈ 2 cm).
__

Realgar (As₄S₄) crystals from Morocco (f.o.v. ≈ 2 cm).
__

Dumortierite rods of unknown origin (f.o.v. ≈ 8 mm).
__

Madagascan iridescent ammonite (f.o.v. ≈ 25 mm).
__

Pentagonite from Wagholi, Pune, India (f.o.v. ≈ 15 mm).
__

Etched slice of the Mounionalusta iron nickel meteorite. Impact was a million of years ago in nowadays Sweden (f.o.v. ≈ 27 mm).
__

__
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.

Pink erythrite crystals besides quartz on Bi-Co-Ni ore from the Bergkappe mine shaft in Schneeberg, Germany (f.o.v. ≈ 17 mm).
__

Scarlet cinnabar (HgS) with yellow siderite (FeCO₃) and quartz from the Erzberg, Austria (f.o.v. ≈ 12 mm).
__

Layered sediments of lime stone in the Egyptian White Desert intercalate dust and sand grains (f.o.v. ≈ 1 cm).
__