Gray, this color has mainly the main dolomite (CaMg (CO3)2). It can be found most frequently on the gravel banks of the Tyrolean Lech.
As one of the oldest rocks, the main dolomite was formed about 220 million years ago, mainly in the lagoons and tidal flats of the Tethys Sea. Thin mats of blue-green algae formed under high salinity and high temperatures. Few animals and plants populated these areas, so fossils in the main dolomite are a rarity.

The white lines in the gray main dolomite are small, white calcite crystals. They have become embedded in the fissures formed by the fracturing of the main dolomite during the folding of the Alps. Along these veins, the main dolomite easily disintegrates into the coarse gravel. The rugged weathering gives rise to the characteristic summit formations. Extensive alpine pastures are missing, because the soil formation above this source rock is only slight.

If you break the main dolomite, you can easily recognize it by the typical smell of crude oil. A greeting from times long past - the intense scent comes from the organic components of the fossilized blue-green algae.