English: Scanned image of thin section from Siilinjärvi apatite ore in cross polarised transmitted light.

The thin section presents apatite-rich carbonate ore. The grain size is quite big and the thin section consist mostly of big apatite grains in granular carbonate mass. The sample is not oriented. The grains are mostly anhedral.

Carbonates form the groundmass in the sample and 55 % of the thin section area. Calcite is more common carbonate mineral than dolomite. Carbonates form mineral aggregates with granoblastic texture, and the grain size varies in the sample. Dolomite grains are commonly smaller than calcite grains. The biggest grains are 3 mm in diameter. The grains in the aggregates are less than 1 mm in diameter, and regionally the grains in the aggregates can be less than 0.2 mm in diameter.

Apatite is present as large porphyroclasts that form 30 area-% of the thin section. Rouded grains are commonly slightly elongated, and have some carbonate inclusions which are oriented along the fractures planes. Grain diameter varies normally between 1 and 4 mm.

Tetraferriphlogopite forms 15 area-% of the thin section. Grains are usually large, but some broken pieces are also present. The biggest flake is 8 mm long and 2 mm wide, while the average grain is about 2 mm long and 1 mm wide.