A metamorphic rock, formed by the metasomatism of pre-existing carbonate rocks (limestone or dolostone).
Here's a breakdown of the key aspects of its composition:
1. Primary minerals:
* Calcite (CaCO3) and dolomite (CaMg(CO3)2) are the original carbonate minerals.
* Garnet (various compositions, like grossularite, andradite, etc.), pyroxene (diopside, hedenbergite, etc.), amphibole (hornblende, actinolite, etc.), epidote are common minerals formed during metasomatism.
* Iron oxides (magnetite, hematite) are also often present.
2. Influence of the metasomatic fluid:
* The chemical composition of the metasomatic fluid (often hydrothermal fluids related to igneous activity) plays a significant role in the specific mineral assemblage of the skarn.
* For example, a fluid rich in iron will lead to the formation of iron-rich minerals like andradite garnet and hedenbergite pyroxene.
* Fluids rich in aluminum can result in the formation of grossularite garnet.
3. Other factors:
* Temperature and pressure during metasomatism influence the mineral assemblage.
* The original composition of the carbonate rock also plays a role.
4. Key point:
Skarn is essentially a metamorphic rock where the original carbonate minerals have been replaced by a diverse range of new minerals formed due to the interaction with a metasomatic fluid. The exact chemical composition depends on the specifics of the geological environment where it formed.
5. Example:
A skarn formed from a limestone with a high iron content and a metasomatic fluid rich in silica might contain minerals like andradite garnet, hedenbergite pyroxene, and quartz.
In summary: Skarn is a complex rock, and its chemical composition is highly variable, but it's generally defined as a metamorphic rock formed by the metasomatism of pre-existing carbonate rocks. The specific mineral assemblage depends on factors such as the composition of the metasomatic fluid, temperature, pressure, and the original composition of the carbonate rock.
