File:Thin section scan crossed polarizers Siilinjärvi R616-78.20.jpg

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

The thin section has a well-developed foliation and plenty of apatite. The thin section is highly sheared, and the mineral grains have shattered to small fragments. Shearing has concentrated to the mica-rich zones.

Common phlogopite is present as uniformly oriented elongated laths. Bigger flakes are almost completely broken into pieces, but some grains still remain in the apatite rich zones. Lots of mineral fragment, mostly apatite, are found in the mica flow area, apart from the most powerful shear zones. Common phlogopite forms half of the thin section area and the grains vary in size with the shearing intensity. Usually the elongated grains are 0.1-0.5 mm long, and less than 0.1 mm wide.

Apatite covers 35 % of the thin section and is present almost all over the thin section. It is commonly in contact with carbonates, but much of the apatite is also as individual fragments in the mica groundmass. The biggest grains, though already broken, are > 5 mm in diameter. More common is the size of the fragments, 0.1-0.5 mm in diameter.

Carbonates form 15 area-% of the thin section, and both carbonate minerals are present. Calcite is more common in contact with the apatite grains, and dolomite as small scale aggregates in the mica flow. Carbonate grains are < 0.5 mm, often 0.05-0.2 mm in diameter.