Return to Alkaline Rocks
Fenites are Na- and K-rich silicate rocks developed at the contact of alkaline igneous intrusions and their surrounding country rocks. Fenites are not necessarily confined to the intrusive contact and may develop at a significant distance from the intrusion through interaction of the country rock with percolating fluids, or inside the intrusion through reaction of xenoliths with their entraining magma. Fenites typically comprise potassium feldspar, albite, aegirine, various sodic amphiboles and, in some cases, nepheline. A variety of more exotic silicate, phosphate and oxide minerals (like narsarsukite, fluorcaphite and strontiopyrochlore) can be found in these rocks. One example of such a mineralogically interesting fenite is described in this paper.
[Upper right] Fine-grained massive variety of fenite from Lovozero (Kola), developed after quartzite. This rock is sometimes used for making knick-knack boxes and, presumably, is a popular hangout for small tundra dwellers (look in the left upper corner for evidence).
[Lower right] Coarse-grained fenite developed at the contact between carbonatite (white, at right) and syenite at Eden Lake (Manitoba). This variety is the product of complete recrystallization of the fine-grained precursor rock (alkali feldspar syenite) to a mixture of microcline (pink) and aegirine-augite (black).