Hydrothermal Calcite

Wonderful geometries in calcite crystals


This image is a close-up view of large calcite crystals. The presence of the coloured bands is due to twinning: what  appears to the naked eye to be compact crystals, 


 when seen under a microscope reveals internal layers in which the atoms are distributed differently from those of the encasing crystal, and which therefore refract light differently, creating variable interference colours.


These calcites were found in a sedimentary formation that dates to approximately 240 million years ago, but they can also be found in other “vessels”.


In fact, this calcite does not have sedimentary origins but hydrothermal: once the rock was formed, hot water with a high mineral salt content flowed over the fractures and cavities, filling them with minerals such as calcite.


This calcite was formed together with galena and blende (or sphalerite),minerals that were extracted at Col Piombin up until the start of the last century 


for the production of zinc, lead and iron. References: http://en.wikipedia.org/wiki/Sphalerite




Name: Hydrothermal Calcite
Classification: Hydrothermal mineral
Mineral composition: Calcite, Dolomite, Galena, Blende, Pyrite, other
Fossils: none
  Location: Col Piombin in the vicinity of Passo Giau (46°28’36.2″N 12°03’42.8″E)
Formation: Contrin formation
Upper Anisic (approximately 242 million years ago)
Depositional environment*:

Piattaforma carbonatica (ambiente di mare basso sotto costa)

*) The environment refers to the encasing rock and not the calcite that is the subject of the photo