File:Thin section scan crossed polarizers Siilinjärvi R636-136.45.jpg

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

The thin section is not that clearly oriented and has a lot of opaque minerals. Carbonates are concentrated to the middle of the thin section. Richterite amphibole forms three different vein-like structures crosscutting the thin section.

Tetraferriphlogopite forms 50 area-% of the thin section. It is mostly present as 0.5-3 mm wide flakes, but there are also smaller elongated chips. Small grains are found within more sheared places and between the larger flakes. The chips are oriented and less than 1 mm long.

Carbonates form 13 area-% of the thin section, but they are mainly found only in one region. There they form granular aggregates, and the common diameter of individual grains is 0.5-1.5 mm. Calcite is the dominating carbonate mineral, although some small grains of dolomite are present.

Richerite amphiboles are found normally as > 1 mm long grains, and the biggest ones are > 4 mm long. They form 10 are-% of the thin section and are often found in companion with apatite and carbonates. Grains are often elongated and broken along the boundaries.

The thin section contains 8 area-% of opaques, which are 0.5-3 mm in diameter. They are probably mostly magnetite, pyrrhotite and pyrite according to the grain shape and MLA-results. Apatite is quite rare, and it forms only 3 % of the thin section area. The biggest grains are > 2 mm, but normally the grains are < 1 mm in diameter. The grains are rounded and contain some inclusions of micas and carbonates.

Unidentified uniaxial pyroxene looking mineral forms 2 area-% of the thin section. The biggest grains are almost 5 mm in diameter, but some grains are broken into small pieces. The grains are anhedral and contain mica inclusions. This mineral is probably the Mg-Fe silicate found in EPMA-analyses, so it could be serpentinised bronzite.