Ore Minerals in Reflected Light

(Width of field is indicated)

Native gold between pyrite and galena. Gold and galena occur also along veinlets within pyrite. Pataz. Peru. Parallel nicols. 0.53 mm.

Native gold as interstitial filling in part in tiny cavities in arsenopyrite, partly idiomorphic. Giant Mine, Yellowknife, Northwest Territory. Canada. Parallel nicols. 0.66 mm

Native silver, löllingite (euhedral), arsenopyrite and sphalerite in a carbonate gangue. Chañarcillo. Chile. Parallel nicols. 0.53 mm.

Exsolutions of ilmenite and ulvospinel in magnetite. Taberg. Sweden. Parallel nicols. 0.21 mm.

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Exsolution of magnetite and ulvospinel within two adjacent grains of ilmenite. Sanford Lake, New York. USA. Parallel nicols, Oil immersion. 0.26 mm

Same photo as above. Sanford Lake, New York. USA. Crossed nicols. 0.26 mm.

Martitization, Observe hematite replacing euhedral magnetite. El Laco. Chile. Parallel nicols. 0.53 mm

Specular hematite. Spain. Parallel nicols. 0.66 mm.

Same photo as above. Observe the blood-red internal reflections. Spain. Crossed nicols. 0.66 mm.

Idiomorphic grains of chromite (dark gray) cemented by nickeline (orange), rammelsgergite (white) and ilmenite (mineral in the center more reflective than chromite). Los Jarales, Ronda Peridotita.

Subhedral chromite crystals (dark gray) and insterstitial nickeline grains. Note single ilmenite grain (gray) with minute inclusions of magnetite (a little ligther). La Gallega, Ronda Peridotite, Spain. Section FE-83-1, parallel nicols , width 1,06 mm.

Rutile grain showing the typical lamellae twinning. Chisel Lake, Manitoba, Canada. Parallel nicols, Oil immersion. 0.21 mm.

Same photo as above. Observe the strong internal reflections. Chisel Lake, Manitoba, Canada. Crossed nicols. 0.21 mm.

Euhedral arsenopyrite with pyrrhotite, pyrite and sphalerite. Dale Head, North vein. England. Parallel nicols. 1.33 mm.

Bornite being replaced by chalcocite and hematite (strong relief), relictic pyrite is also present. Buena Esperanza. Chile. Parallel nicols. 0.88 mm.

Digenite (blue) and chalcocite mantling bornite grains. Hematite crystals (whitish) at the upper left part and, with an atypical bluish color in the center, within the chalcocite. Carolina de Michilla. Chile. Parallel nicols. 0.53 mm.

Lamellae grains of covellite replacing enargite and in part pyrite. Yauricocha. Peru. Parallel nicols. 0.66 mm.

Same photo as above. Yauricocha. Peru. Crossed nicols. 0.66 mm.

Chalcopyrite (yellow) and cubanite (light brown) enclosing elongated pyrrhotite (pinkish) grains. Komori Mine Japan. Section OM-252, parallel nicols,width 1.06 mm.

Same photo as above but with crossed nicols and rotated. Note the light blue anisoptropy of cubanite.

Covellite almost monomineralic in fine elongated grains. Yauricocha. Peru. Parallel nicols. 2.13 mm.

Same photo as above. Yauricocha. Peru. Crossed nicols. 2.13 mm.

Pyrite and magnetite in pyrrhotite. Obseve the pyrrhotite bireflection (reflection pleochroism). Ducktown, Tennessee. USA. Parallel nicols. 2.13 mm.

Iron poor translucent colloform sphalerite (Schalenblende). Wiesloch. Germany. Parallel nicols. 2.65 mm

Same photo as above. Wiesloch. Germany. Crossed nicols. 2.65 mm.

Rhomb-shaped areas of deeply etched hexagonal pyrrhotite (lower 'reflectance, mottled brown-grey, centre and top right) are surrounded by more lightly etched monoclinic pyrrhotite, which is the main phase. Very lightly etched monoclinic pyrrhotite (pale brown, bottom right) has a rim of granular pentlandite (light brown, higher reflectance, bottom right). Pyrrhotite is intergrown with chalcopyrite (yellow, centre) and encloses subhedral magnetite (grey, top left), some of which is lightly etched (left bottom). Polished block (etched with HI), plane polarized light, air

250 μm

Chalcopyrite (yellow, centre) is intergrown with silver-bearing tetrahedrite (light grey-green, bottom centre). A single crystal of pyrite (light yellow-white, top centre) is enclosed within chalcopyrite. Dolomite rhombs (medium grey, top right), euhedral quartz (centre left) and chlorite (bottom right) are the gangue minerals.

250μm

Coarse-grained cassiterite (light grey, left) is intergrown with radiating laths of molybdenite which show bireflectance and reflection pleochroism (brown-grey to grey, top right). The main silicates are coarse-grained white mica with cleavage (top left) and quartz (bottom right). Black areas are polishing pits.

250 μm

Coarse blades and laths of molybdenite show strong bireflectance and reflection pleochroism. The strong basal cleavage of molybdenite (left) parallel to (0001) is clearly seen, as are deformation effects similar to kink banding (centre). The dark grey area (bottom) is quartz. Four trigonal carbonate crystals showing bireflectance are lighter grey (bottom left). Black areas are polishing pits. Polished block, plane polarized light, air

500 μm

Heazlewoodite (white, centre), the main phase, encloses a small rounded crystal of nickel arsenide (pink, lower reflectance, centre left) and is altered along fractures and grain boundaries to millerite (light yellow-brown, lower reflectance, centre right). Black areas are serpentine. Polished thin section, plane polarized light, oil

125 μm

This is the same field of view as previous section but with partially crossed polars. The strong anisotropy of heazlewoodite (blush-pink and blue-grey) and extreme anisotropy of millerite (golden yellow to deep blue) are visible. Millerite forms along the fractures in heazlewoodite but is associated with a phase with less intense anisotropy colours (orange-brown, left centre to blue-grey, centre right) which has the optical properties of godlevskite. Blue-green internal reflections of serpentine arc striking. Polished thin section, partially crossed polars, oil

125 μm