File:Thin section scan crossed polarizers Siilinjärvi 501-M3.jpg

English: Scanned image of thin section from Siilinjärvi apatite ore M3 in cross polarised transmitted light.

The thin section can be divided into two domains: about half of the area consists of carbonate domains and rest of mica domains. The mica domains are sheared and have a nematoblastic texture. The shearing is also visible in the carbonate domains, but not that clearly. The carbonate domains show heterogranular texture. Feldspars are found as rare accessory mineral.

Carbonates form 50 area-% of the sample and they are grouped into domains that are as wide as the whole section and consist almost purely of carbonates. Calcite is slightly more common carbonate mineral than dolomite, and some veins consist only of calcite. The grain size varies quite lot, the biggest grains are > 2 mm in diameter and smallest ones well < 0.1 mm. The grains are moderately altered and slightly elongated to the mica shear direction. The grains are rounded and the aggregates have a granular texture.

Common phlogopite flakes form 45 area-% of the thin sections. The grains are very elongated and some mica fishes are present. The grains are commonly < 0.1 mm wide and the average grain is 0.3 mm long. The grains are oriented in the same direction as the different domains in the sample. The mica domains are not as monomineralic as the carbonate domains, because apatite, carbonate and opaque grains are also present.

Most of the apatite in the sample occurs in small carbonate-apatite veins inside the mica domains, and the mineral forms 5 area-% of the sample. The grains are quite small (less than 0.3 mm in diameter) and rounded. Some individual apatite grains are also present in the phlogopite rich zones. Apatite is not present in the carbonate domains.