SCHREIBERSITE
Schreibersite – (Fe,Ni)3P – is a native element that occurs in meteorites and in only two terrestrial geological occurrences. It’s not ore.
1. Characteristics
Crystal system: Tetragonal bisphenoidal.
Color: From silver-white to tin-white, it tarnishes toward brass-yellow or toward brown.
Habit: Acicular or droplike shapes when occuring as inclusions in cohenite. Crystals are rare.
Cleavage: {001} perfect, {010} imperfect, {110} imperfect.
Tenacity: Very brittle.
Twinning: No information available.
Fracture: No information available.
Mohs Hardness: 6.5 – 7
Parting: No.
Streak: No information available.
Lustre: Metallic.
Diaphaneity: Opaque.
Density (g/cm³): 7.0 – 7.3
2. Geology and Deposits
Schreibersite is found in virtually all Fe-Ni meteorites and also occurs in some stony meteorites.
It is present in basalts that formed under extremely reducing conditions after intruding into coal seams – for example, on Disko Island (Greenland). It occurs as inclusions within cohenite, appearing as oriented acicular (needle-like) crystals in the native iron deposits of Ovifak, which is the only known terrestrial occurrence.
It has also been found in fossilized (petrified) wood, following hydrothermal replacement, at a depth of 1.4 km in the Red Sea.
3. Mineral Associations
In occurrences of native iron within basalts, it is associated with:
– rock-forming silicates (olivine, augite, plagioclase),
– Fe-Ti oxides (ilmenite, magnetite),
– alteration minerals (goethite, kaolinite, montmorillonite, calcite, aragonite, quartz),
– sulfides (pyrite, pyrrhotite, molybdenite, sphalerite), and
– minerals specific to this paragenesis, such as native iron, wüstite, cohenite, and taenite.
4. Transmitted Light Microscopy
Not applicable, as schreibersite is completely opaque.
The literature states that schreibersite is uniaxial.
5. Reflected Light Microscopy
Sample preparation: The polishing hardness of schreibersite is approximately the same as that of native iron, and slightly higher than that of cohenite.
PLANE POLARIZED LIGHT – PPL
Reflection color: Light cream to white.
Compared to the color of cohenite, the color of schreibersite is lighter.
Compared to the color of native iron, the color of schreibersite in its lightest orientation is very similar.
Pleochroism: No.
Reflectivity: ~52%
Bireflectance: No.
CROSSED POLARIZED LIGHT – XPL
Isotropy / Anisotropy: Weak anisotropy in brownish-gray tones.
Internal reflections: No.
May be confused with: No information available.
General Characteristics:
Grain shape: occurs as inclusions within cohenite, in the form of oriented acicular shapes, in the native iron occurrences at Ovifak – the only known terrestrial occurrence.
