Ijolite

Foidolites are coarse-grained intrusive igneous rock with a feldspathoid mineral content greater than 60%. On the APF diagram, these rocks plot in the corner closest to F. The term "foidolite" is too general and, wherever possible, should be replaced with a name that clarifies which of the feldspathoid minerals is predominant and whether other minerals are present in any significant amount. For example, nephelinolites are foidolites comprising mostly nepheline; they can be further categorized as melteigite, ijolite or urtite depending on the relative proportion of dark-colored minerals (most of all, clinopyroxene and biotite) in their composition.
The volcanic equivalents are termed foidite and phonolitic or tephritic foidites. According to the mineralogy can be divided into:

• Ferusite For Fergus, Montana, USA: A variety of foidolite containing essential clinopyroxene and 30-70% modal leucite (typically replaced by a mixture of nepheline, alkali feldspar, kalsilite and analcime).
• Ijolite For Iijoki, northern Finland: A variety of foidolite containing essential clinopyroxene (diopside, aegirine-augite or aegirine) and 30-70% modal nepheline.
• Italite For Italy: A variety of foidolite in which leucite is the predominant feldspathoid mineral and ferromagnesian silicates comprise 30 modal % or less of the rock.
• Melilitite For Melteig, Norway: A collective name for extrusive and shallow intrusive rocks containing > 10% modal melilite, devoid of kalsilite and, if other feldspathoid minerals are present, F < melilite.
• Missourite For Missouri, USA: A variety of foidolite containing essential clinopyroxene and 10-30% modal leucite; olivine is also commonly present.
• Tawite For Tavajok, Lovozero Mts., Kola, northwestern Russia: A variety of foidolite in which sodalite is the predominant feldspathoid mineral.
• Urtite For Lujavr Urt, Lovozero Mts. Kola, northwestern Russia: A variety of foidolite containing > 70% modal nepheline; clinopyroxene, apatite, titanite, magnetite and perovskite are commonly present in subordinate amounts.

Samples doned by F.Stoppa (Chieti University, Italy).

Bibliography



• Ron H. Vernon (2004): A pratical guide to rock microstructure. Cambridge editore
• Eric A.K.Middlemost (1985): Magmas and Magmatic Rocks. Longman, London
• Ron H. Vernon (2004): A pratical guide to rock microstructure. Cambridge editore


Photo
ijolite(canarie)(1).jpg

Aegirine (green), altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. PPL image, 2x (Field of view = 7mm)
ijolite(canarie)(2).jpg

Aegirine, altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. XPL image, 2x (Field of view = 7mm)
ijolite(canarie)(3).jpg

Aegirine (green), titanite, altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. PPL image, 2x (Field of view = 7mm)
ijolite(canarie)(4).jpg

Aegirine, titanite, altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. XPL image, 2x (Field of view = 7mm)
ijolite(canarie)(5).jpg

Aegirine (green), altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. PPL image, 2x (Field of view = 7mm)
ijolite(canarie)(6).jpg

Aegirine (green), titanite, altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. PPL image, 2x (Field of view = 7mm)
ijolite(canarie)(10).jpg

Aegirine (green), altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. PPL image, 2x (Field of view = 7mm)
ijolite(canarie)(11).jpg

Aegirine, altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. XPL image, 2x (Field of view = 7mm)
ijolite(canarie)(12).jpg

Aegirine (green), altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. PPL image, 2x (Field of view = 7mm)
ijolite(canarie)(13).jpg

Aegirine, altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. XPL image, 2x (Field of view = 7mm)
ijolite(canarie)(14).jpg

Aegirine (green), altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. PPL image, 2x (Field of view = 7mm)
ijolite(canarie)(15).jpg

Aegirine (green), altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. PPL image, 2x (Field of view = 7mm)
ijolite(canarie)(16).jpg

Aegirine (green), altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. PPL image, 2x (Field of view = 7mm)
ijolite(canarie)(17).jpg

Aegirine (green), altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. PPL image, 2x (Field of view = 7mm)
ijolite(canarie)(18).jpg

Aegirine (green), titanite, altered nepheline and feldspar (dusty). Caletta de la cruz, Fuerteventura, Canary Islands. PPL image, 2x (Field of view = 7mm)