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

The thin section has a very low amount of small mica chips. The bigger mica flakes in the sample are oriented, but shearing has not affected the grain size nor formed any foliation. Magnetite is found as accessory mineral in the thin section.

Tetraferriphlogopite forms 75 area-% of the sample and is mostly present as somewhat elongated flakes. The grains are usually 1-2 mm long and 0.3-1.5 mm wide. Smaller chips are in minority and do not show any orientation.

Amphiboles look often quite broken, but usually the grains still appear large. The blue colour is quite weak, but still prominent. The amphiboles are a mixture between richterite and tremolite. The biggest grains are > 7 mm in diameter and have inclusions of micas and apatites. Some smaller (diameter 0.3-1.5 mm) euhedral grains are also present. Amphiboles form 10 area-% of the thin section.

Carbonates look quite pure in the thin section and they are grown into large mineral aggregates. The aggregates have other mineral grains in them, mostly apatite. Carbonate grain size varies a lot, and the biggest grains are usually found in the middle of the granular aggregates (diameter almost 2 mm). The aggregate margins feature smaller grains. Carbonates are also quite common as small individual grains in the mica groundmass. Calcite is more common carbonate mineral in the aggregates, dolomite as individual grains. Carbonates form 8 area-% of the thin section.

Apatite is found in companion with carbonates and forms 7 area-% of the thin section. Mostly the apatite is present as big rounded grains together with carbonates, but there is also a lot of small apatite pieces in the mica groundmass. Average sized apatite is 1-3 mm in diameter, the pieces in the groundmass are 0.1-1 mm in diameter.