File:Thin section scan crossed polarizers Siilinjärvi R276-108.40.jpg

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

The sample is highly sheared, and the shearing in concentrated into micas. Almost the whole sample show a flow structure, the only exception is a carbonate mineral domain in the other side of the thin section.

Common phlogopite forms 70 area-% of the thin section. The mineral has deformed and sheared to small elongated flakes. Some larger grains has remained, but mostly the mica is found as small elongated chips. The average grain size is hard to specify because it varies so much, but commonly the elongated chips at the shear zones are about 0.3 mm long and less than 0.1 mm wide.

Richterite amphiboles are concentrated into one vein-like structure which cross-cuts the thin section. The amphiboles form 15 area-% of the thin section and the subhedral grains are usually quite big (up to 4 mm in diameter), but broken into smaller pieces. The grains have a lot of inclusions.

Carbonates are not that common in the thin section, but calcite has formed a vein-like structure in the other side of the thin section. The texture of the structure is granular and it consist dominantly of carbonates. The grain size is on average 1 mm in diameter. The phlogopite has penetrated this structure from the sides, and in these spots apatite is present. Some pieces of calcite occur in the flow zones, but it is not that abundant. Carbonates form 10 area-% of the thin section.

Pieces of apatite are found all over the sample, but they are more frequent near the richterite grains. The large apatite grains are filled with some small inclusions. Apatite forms 5 area-% of the thin section. The grain size is usually quite small, but some non-broken grains are > 1 mm in diameter.