In petrology, limburgite is a dark-colored

volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic ...

resembling

basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...

in appearance, but containing normally no

feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...

. The name derives from the type locality the Limberg or the Limburg, close to Sasbach am Kaiserstuhl in Baden-Württemberg, where they occur in the well-known rock of the Kaiserstuhl. They consist essentially of

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

and augite with a brownish glassy

groundmass The matrix or groundmass of a rock is the finer-grained mass of material in which larger grains, crystals, or clasts are embedded. The matrix of an igneous rock consists of finer-grained, often microscopic, crystals in which larger crystals, ...

. The augite may be green, but more commonly is brown or violet; the olivine is usually pale green or colourless, but is sometimes yellow. Within the groundmass a second generation of small euhedral augites frequently occurs; more rarely olivine is present also as an ingredient of the matrix. The principal accessory minerals are

ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing ...

and apatite. Feldspar though sometimes present, is never abundant, and

nepheline Nepheline, also called nephelite (), is a rock-forming mineral in the feldspathoid groupa silica-undersaturated aluminosilicate, Na3 K Al4 Si4 O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatite ...

also is unusual. In some limburgites large

phenocryst 300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter ...

s of dark brown

hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rock ...

and biotite are found, mostly with irregular borders blackened by resorption; in others there are large crystals of

anorthoclase The mineral anorthoclase ((Na,K)AlSi3O8) is a crystalline solid solution in the alkali feldspar series, in which the sodium-aluminium silicate member exists in larger proportion. It typically consists of between 10 and 36 percent of KAlSi3O8 and ...

Hauyne Hauyne or haüyne, also called hauynite or haüynite ( ), is a tectosilicate sulfate mineral with endmember formula . As much as 5 wt % may be present, and also and Cl. It is a feldspathoid and a member of the sodalite group. Hauyne was fir ...

is an ingredient of some of the limburgites of the Cape Verde Islands.- Rocks of this group occur in considerable numbers in Germany (Rhine district) and in Bohemia, also in

Scotland Scotland (, ) is a Countries of the United Kingdom, country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a Anglo-Scottish border, border with England to the southeast ...

Auvergne Auvergne (; ; oc, label= Occitan, Auvèrnhe or ) is a former administrative region in central France, comprising the four departments of Allier, Puy-de-Dôme, Cantal and Haute-Loire. Since 1 January 2016, it has been part of the new region Au ...

Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...

, Africa (

Kilimanjaro Mount Kilimanjaro () is a dormant volcano in Tanzania. It has three volcanic cones: Kibo, Mawenzi, and Shira. It is the highest mountain in Africa and the highest free-standing mountain above sea level in the world: above sea level and a ...

) and

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

. They are associated principally with basalts, nepheline and

leucite Leucite is a rock-forming mineral of the feldspathoid group, silica-undersaturated and composed of potassium and aluminium tectosilicate KAlSi2O6. Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster in ...

basalts and

monchiquite Lamprophyres () are uncommon, small-volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks, and small intrusions. They are alkaline silica- undersaturated mafic or ultramafic rocks with high magnesium ...

s. From the last-named rocks the limburgites are not easily separated as the two classes bear a very close resemblance in structure and in mineral composition, though many authorities believe that the ground mass of the monchiquites is not a glass but crystalline

analcite Analcime (; ) or analcite is a white, gray, or colorless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is Na Al Si2 O6· H2O. Minor amounts of potassium and calci ...

. Limburgites may occur as flows, as sills or dykes, and are sometimes highly vesicular. Closely allied to them are the augitites, which are distinguished only by the absence of olivine; examples are known from Bohemia, Auvergne, the Canary Islands and Ireland.

References

* Volcanic rocks {{igneous-petrology-stub

See also

References