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

In the thin section apatite is mostly found as big inclusions in carbonate aggregates. The thin section has also a couple of narrow carbonate veins and a clear flow structure.

Tetraferriphlogopite forms 70 area-% of the thin section. The grains are often quite broken and bent, but still, grains almost 5 mm wide are found. Small elongated chips form one third of the mica area, larger flakes two thirds. Flakes are usually 1-5 mm long, chips < 1 mm and more elongated.

Apatite appears as large rounded grains in companion with carbonates and forms 10 area-% of the thin section. The grains have carbonate inclusion trails. The diameter of the grains is 1-4 mm.

Carbonates form large aggregates in the thin section and 10 % of the area. Calcite is the dominating carbonate mineral. Grain boundaries are sometimes hard to distinguish because of the dustiness of the grain surfaces and small grain size. Usually the grains are < 1.5 mm in diameter, at the aggregate margins smaller than that.

Amphiboles form 10 area-% of the thin section, and are commonly found as small euhedral grains in the groundmass. The grains are altered into magnetite and < 1 mm in diameter. A few elongated small grains and one large grain > 1 cm long are also present.