Foide
Foids (feldspatoids, representatives of feldspar) are minerals that occur in igneous rock where there is a lack of silica , that is, they are SiO 2 -undersaturated.
Foids occur in alkali-rich silicate melts and in felsic magmatites when the silicic acid content is no longer sufficient to form feldspars rich in silica with aluminum and the alkali metals sodium or potassium .
Foids cannot be found together with quartz in a rock, since feldspars would form until the silicon dioxide is completely used up .
Minerals of the Foid Group
- Leucite KAlSi 2 O 6
- Nepheline (Na, K) AlSiO 4
- Sodalite Na 8 Al 6 Si 6 O 24 Cl 2
- Nosean Na 8 Al 6 Si 6 O 24 (SO 4 )
- Cancrinite Na 6 Ca 2 Al 6 Si 6 O 24 (CO 3 ) 2
- Analcime NaAlSi 2 O 6 · H 2 O
Web links
- Mineral Atlas: Foide (Wiki)