File:Thin section scan crossed polarizers Siilinjärvi H2.jpg

English: Scanned image of thin section from Siilinjärvi apatite ore in cross polarised transmitted light. The thin section was made from a hand sample from the Saarinen area, from the southern-central part of the pit.

The thin section is highly sheared, but shearing is concentrated to micas. Both apatite and carbonates look remarkably well-preserved and they are grouped into domains. Rutile appears in the thin section as post-kinematic mineral in the highly sheared mica zones.

Common phlogopite forms 60 area-% of the thin section. The mineral has deformed and sheared into small elongated flakes. Usually the flakes are < 0.2 mm long and 0.05 mm wide. Rutile has been introduced into the sheared mica zones in a disorderly manner as small rounded subhedral grains, < 0.1 mm in diameter. Rutile forms 2 area-% of the thin section.

Carbonates and apatite form domains with granular, mosaic texture. They are both present in the mica shear zones as small porphyroclasts. Carbonates form 20 area-% and apatites 18 area-% of the thin section. Calcite is the dominating carbonate mineral. The biggest calcite grains are < 2 mm in diameter, common size is about 1 mm in diameter. Apatite grains are smaller, commonly < 0.5 mm in diameter. The shearing is not easy to distinguish from these mineral grains, but the carbonate-apatite domains are grown into the vein-like structures, that are oriented into the mica shear direction. Apatite grains do not have any cracks and inclusions are rare. Some dolomite-calcite intergrowths were also found in the thin section.